Noise filter and electronic device using noise filter

ABSTRACT

Comprising a magnetic member  32  formed by laminating magnetic sheets  24, 28, 30, 31  a first impedance element  21  formed in the magnetic member  32,  and a second impedance element  25  formed above the first impedance element  21,  the first impedance element  21  includes a first normal impedance element  22  and a first common impedance element  23,  and the second impedance element  25  includes a second common impedance element  26  and a second normal impedance element  27.

TECHNICAL FIELD

[0001] The present invention relates to a noise filter used as noise countermeasure in cellular phone or other information devices, and an electronic device using this noise filter.

BACKGROUND ART

[0002] A conventional noise filter is disclosed, for example, in Japanese Laid-open Patent No. 8-335517.

[0003]FIG. 35 is a perspective exploded view of the conventional noise filter (laminated common mode choke coil). A first coil 1 and a second coil 2 formed above the first coil 1 are spirally formed, and made of silver.

[0004] An insulating sheet 3 is formed beneath the first coil 1, and is provided with two via holes 4, 5. A second insulating sheet 6 is formed between the first coil 1 and second coil 2, and is provided with one via hole 7. The first insulating sheet 3 and second insulating sheet 6 are made of insulating material such as polyimide.

[0005] A first external electrode 8 disposed at one end of the first coil 1, and a first via electrode 8 a at other end of the first coil 1 are formed on the same plane as the first coil 1. A second external electrode 9 is formed beneath the first insulating sheet 3. A second via electrode 9 a is formed beneath the first insulating sheet 3, and the second external electrode 9 is connected to the first via electrode 8 a through the via hole 4 provided in the first insulating sheet 3, second via electrode 9 a, and a first leading-out portion 10 formed beneath the first insulating sheet 3.

[0006] A third external electrode 11 provided at one end of the second coil 2, and a third via electrode ha provided at other end of the second coil 2 are formed on a same plane as the second coil 2.

[0007] A fourth external electrode 12 is provided beneath the first insulating sheet 3. A fourth via electrode 12 a is formed beneath the first insulating sheet 3, and the fourth external electrode 12 is connected to the second coil 2 through the via hole 7 formed in the second insulating sheet 6, via hole 5 formed in the first insulating sheet 3, fourth via electrode 12 a, and a second leading-out portion 13 formed beneath the first insulating sheet 3. That is, the second external electrode 9 and fourth external electrode 12 are formed on a same plane. The first external electrode 8, second external electrode 9, third external electrode 11, and fourth external electrode 12 are partly exposed to the end surface of the first insulating sheet 3 and second insulating sheet 6.

[0008] A specified number of third insulating sheets 14 are formed beneath the second external electrode 9 and fourth external electrode 12 and above the first coil 1, and are made of ferrite.

[0009] In this conventional noise filter, when a common mode noise is applied to the first coil 1 and second coil 2, the impedance values of the coils 1, 2 are raised, and the common mode noise is removed.

[0010] In the conventional noise filter, however, the common mode impedance cannot be raised higher.

[0011] That is, end portions of the first coil 1 and second coil 2 (the second external electrode 9 connected to the first coil 1 and fourth external electrode 12 connected to the second coil 2) are drawn out in the same direction (downward). It hence leads to possibility of short-circuiting of the via holes 5 and 7 for connecting the first via electrode 8 a formed in the first coil 1, second coil 2, fourth via electrode 12 a, and fourth external electrode 12. If short-circuited, the first coil 1 and second coil 2 are electrically connected, and the common mode noise removing characteristic may not be obtained. It is therefore necessary to keep a certain spacing 15 between the first via electrode 8 a and via hole 7, and a conductor extending from the first coil 1 cannot be provided in this spacing 15 and the first coil 1 and second coil 2 cannot be overlaid in the area corresponding to the spacing 15, and the overlapping region of the first coil 1 and second coil 2 cannot be increased further.

[0012] Moreover, if the current flow directions are reverse in the first coil 1 and second coil 2, the magnetic fluxes generated in the first and second coils cancel each other, and the impedance of normal mode cannot be raised.

[0013] A different conventional common mode noise filter is disclosed, for example, in Japanese Utility Model Publication No. 7-45932.

[0014]FIG. 36 is a perspective exploded view of the conventional common mode noise filter (laminated coil).

[0015] In a main body 201, a first coil and a second coil are formed. Upper and lower electrodes 202 and 203 are disposed on both sides of the main body 201. Magnetic shield layers 204, 205 are provided in the outermost layer of the common mode noise filter. That is, the conventional common mode noise filter is composed of the main body 201, electrodes 202, 203, and magnetic shield layers 204, 205.

[0016] The main body 201 is composed of plural magnetic sheets for first coil 206, 207, 208, and magnetic sheets for second coil 209, 210, 211. The magnetic sheets for first coil 206 to 208 and magnetic sheets for second coil 209 to 211 are alternately disposed.

[0017] Specifically, the magnetic sheet for second coil 211, magnetic sheet for first coil 208, magnetic sheet for second coil 210, magnetic sheet for first coil 207, magnetic sheet for second coil 209, and magnetic sheet for first coil 206 are laminated sequentially from the bottom.

[0018] On the top of the magnetic sheets 206 to 211, conductor patterns for forming the first coil 212, 213, 214, and conductor patterns for forming the second coil 215, 216, 217 are printed in a square shape of nearly one turn.

[0019] A terminal end 212 b of the conductor pattern 212 formed in the magnetic sheet 206 is electrically connected to an initial end 213 a of the conductor pattern 213 formed in the magnetic sheet 207 by way of a through-hole 212 c of the terminal end 212 b and a through-hole 209 a of the magnetic sheet 209.

[0020] Also, a terminal end 213 b of the conductor pattern 213 formed in the magnetic sheet 207 is electrically connected to an initial end 214 a of the conductor pattern 214 formed in the magnetic sheet 208 by way of a through-hole 213 c of the terminal end 213 b and a through-hole 210 a of the magnetic sheet 210.

[0021] Similarly, a terminal end 215 b of the conductor pattern 215 formed in the magnetic sheet 209 is electrically connected to an initial end 216 a of the conductor pattern 216 formed in the magnetic sheet 210 by way of a through-hole 215 c of the terminal end 215 b and a through-hole 207 a of the magnetic sheet 207.

[0022] Further, a terminal end 216 b of the conductor pattern 216 formed in the magnetic sheet 210 is electrically connected to an initial end 217 a of the conductor pattern 217 formed in the magnetic sheet 211 by way of a through-hole 216 c of the terminal end 216 b and a through-hole 214 a of the magnetic sheet 208.

[0023] In this way, the first coil composed of conductor patterns 212 to 214 of magnetic sheets 206 to 208, and the second coil composed of conductor patterns 215 to 217 of magnetic sheets 209 to 211, in the same phase and same number of turns as the first coil, are formed in every other layer.

[0024] The upper electrode 202 is composed of magnetic sheets 218, 219, and 220. On the magnetic sheets 218 to 220, leading-out electrode conductor patterns 221 a, 221 b, 221 c, 222 a, 222 b, 222 c are formed respectively.

[0025] The leading-out electrode conductor patterns 221 a to 221 c are mutually connected by way of through-hole, and are further connected with the initial end 212 a of the conductor pattern 212 of the magnetic pattern 206 for forming the first coil.

[0026] Similarly, the leading-out electrode conductor patterns 222 a to 222 c are mutually connected by way of through-hole, and are further connected with the initial end 215 a of the conductor pattern 215 of the magnetic pattern 209 for forming the second coil.

[0027] In this manner, on the upper electrode 202, a first coil leading-out electrode terminal T1 a, and a second coil leading-out electrode terminal T2 a are formed.

[0028] Further, the lower electrode 203 is composed of magnetic sheets 223, 224, and 225. On the magnetic sheets 223 to 225, leading-out electrode conductor patterns 226 a, 226 b, 226 c, 227 a, 227 b, 227 c are formed respectively. (227 b, 227 c are not shown.)

[0029] The leading-out electrode conductor patterns 226 a to 226 c are mutually connected by way of through-hole, and are further connected with the terminal end 214 b of the conductor pattern 214 of the magnetic pattern 208 for forming the first coil.

[0030] Similarly, the leading-out electrode conductor patterns 227 a to 227 c are mutually connected by way of through-hole, and are further connected with the terminal end 217 b of the conductor pattern 217 of the magnetic pattern 211 for forming the second coil.

[0031] In this manner, on the lower electrode 203, a first coil leading-out electrode terminal T1 b, and a second coil leading-out electrode terminal T2 b are formed.

[0032] In this conventional common mode noise filter, when a common mode noise is applied in the first coil and second coil, the impedance values of the coils are raised, and the common mode noise is removed.

[0033] In the conventional common mode noise filter, however, the common mode impedance cannot be raised further.

[0034] That is, of the square-shaped conductor patterns 212 to 217, for example relating to the pattern 212 for composing the first coil, since the initial end 212 a is formed inside of the terminal end 212 b, the conductor pattern between the initial end 212 a and the folded portion 212 d of the conductor pattern 212 cannot be overlaid on the conductor pattern 215 for forming the second coil in the top view, and therefore the magnetic flux generated by the first coil and the magnetic flux generated by the second coil cannot reinforce each other efficiently.

SUMMARY OF THE INVENTION

[0035] The invention is intended to solve the problems of the prior art, and it is hence an object thereof to present a noise filter of high removing characteristic of both common mode noise and normal mode noise, capable of enhancing the impedance in both common mode and normal mode, and an electronic device using such noise filter.

[0036] It is also an object thereof to present a noise filter of high removing characteristic of common mode noise, capable of enhancing the impedance in the common mode further, and an electronic device using such common mode noise filter.

[0037] To achieve the objects, the noise filter in a first aspect of the invention (embodiments 1, 2 described below) comprises a magnetic member formed by laminating magnetic sheets in vertical direction, a first impedance element formed inside the magnetic member, a second impedance element formed above the first impedance element, and external electrodes formed at both ends of the magnetic member and connected electrically to each end of the first and second impedance elements, in which the first impedance element includes a first normal impedance element and a first common impedance element connected electrically to the first normal impedance element above the first normal impedance element, the second impedance element includes a second common impedance element and a second normal impedance element connected electrically to the second common impedance element above the second common impedance element, and the first common impedance element and second common impedance element are opposite to each other, and are insulated. In this configuration, the impedance value can be heightened in both common mode and normal mode.

[0038] To achieve the objects, the noise filter in a second aspect of the invention (embodiments 3, 4, 5 described below) comprises a magnetic member formed by laminating magnetic sheets in vertical direction, a first coil formed by laminating plural first inner conductors, a second coil formed by laminating plural second inner conductors, and external electrodes formed at both ends of the magnetic member and connected electrically to each end of the first and second coils, in which the magnetic member incorporates a first laminated body composed of the first inner conductors, a second laminated body formed on the top of the first laminated body, having the first inner conductors and second inner conductors laminated alternately, and a third laminated body formed on the top of the second laminated body, composed of the second inner conductors. In this configuration, the impedance value can be heightened in both common mode and normal mode.

[0039] To achieve the objects, the common mode noise filter in a third aspect of the invention (embodiment 6 described below) comprises a magnetic member formed by laminating magnetic sheets in vertical direction, a first coil formed by laminating plural first inner conductors, a second coil formed by laminating plural second inner conductors formed alternately with the first inner conductors, and overlapping with the first coil in a top view of the magnetic member, and plural via holes formed in the magnetic sheets for connecting the first inner conductors mutually or the second inner conductors mutually, in which the via holes for connecting the first inner conductors mutually overlap with the second coil in a top view of the magnetic member, the via holes for connecting the second inner conductors mutually overlap with the first coil in a top view of the magnetic member, and the first inner conductors and at least one of the second inner conductors adjacent to the first inner conductors are formed to overlap almost with each other in a top view of the magnetic member. In this configuration, the impedance value can be heightened more in common mode.

BRIEF DESCRIPTION OF THE DRAWINGS

[0040]FIG. 1 is a perspective exploded view of a noise filter in embodiment 1 of the invention;

[0041]FIG. 2(a) is a sectional view along line A-A of the noise filter;

[0042]FIG. 2(b) is a perspective view of the noise filter;

[0043]FIG. 3(a) is a diagram showing impedance characteristics when current of normal mode and common mode is applied to the noise filter;

[0044]FIG. 3(b) is a diagram showing a measuring circuit of impedance characteristics when current of normal mode and common mode is applied to the noise filter;

[0045] FIGS. 4(a) to (d) are top views of conductors in the noise filter;

[0046]FIG. 4(e) is a sectional view of other example of the noise filter;

[0047]FIG. 5(a) is an equivalent circuit diagram of the noise filter (pattern A);

[0048]FIG. 5(b) is an equivalent circuit diagram of the noise filter (pattern B);

[0049]FIG. 6(a) is a diagram showing impedance characteristics (attenuation characteristics) when normal mode current is applied to the noise filter of pattern A and noise filter of pattern B;

[0050]FIG. 6(b) is a diagram showing the direction of the current applied in each pattern, simulating noise filters of pattern A and pattern B;

[0051] FIGS. 7(a) to (f) are perspective views showing a manufacturing method of the noise filter;

[0052]FIG. 8 is a diagram showing the relation of distance between second conductor and third conductor, coupling coefficient, and withstand voltage of the noise filter;

[0053]FIG. 9 is a sectional view of other example of the noise filter;

[0054]FIG. 10 is a diagram of frequency characteristics showing elevation of impedance value in high frequency region;

[0055] FIGS. 11(a), (b) are sectional views of other example of the noise filter;

[0056] FIGS. 12(a) to (d) are top views of other example of the noise filter;

[0057]FIG. 13 is a sectional view of other example of the noise filter;

[0058] FIGS. 14(a), (b), (d), (e) are top views of conductors of a noise filter in embodiment 2 of the invention;

[0059] FIGS. 14(c), (f) are pattern see-through diagrams of the noise filter;

[0060]FIG. 15(a) is a diagram showing a waveform of carrier in a pair of signal lines in a cellular phone;

[0061]FIG. 15(b) is a diagram showing the manner of use of the noise filter in embodiments 1 and 2 of the invention;

[0062]FIG. 15(c) is a diagram showing attenuation characteristics when the noise filter in embodiments 1 and 2 is used in a pair of signal lines in a cellular phone;

[0063]FIG. 16 is a perspective exploded view of a noise filter in embodiment 3 of the invention;

[0064]FIG. 17(a) is a sectional view of line A-A of the noise filter;

[0065]FIG. 17(b) is a perspective view of the noise filter;

[0066]FIG. 18 is an equivalent circuit diagram of the noise filter in embodiments 3 and 4 of the invention;

[0067]FIG. 19(a) is a diagram showing the relation of the number of turns and coupling coefficient of internal conductors in a second laminated body as the essential part thereof;

[0068]FIG. 19(b) is a diagram showing the relation of the number of turns and coupling coefficient of internal conductors in a first laminated body and a third laminated body as the essential parts thereof;

[0069] FIGS. 20(a) to (g) are perspective views showing a manufacturing method of the noise filter;

[0070]FIG. 21 is a perspective exploded view of the noise filter in embodiment 4 of the invention;

[0071]FIG. 22 is a perspective exploded view of a noise filter in embodiment 5 of the invention;

[0072]FIG. 23(a) is a sectional view of line A-A in FIG. 22;

[0073]FIG. 23(b) is a top see-through diagram of the noise filter;

[0074]FIG. 24 is a sectional view of other example of the noise filter;

[0075] FIGS. 25(a), (b) are top see-through diagrams of other example of the noise filter;

[0076]FIG. 26(a) is a perspective exploded view of other example of the noise filter;

[0077]FIG. 26(b) is a sectional view of line A-A in other example of the noise filter;

[0078]FIG. 27 is an equivalent circuit diagram of the noise filter;

[0079]FIG. 28(a) is a sectional view of the noise filter (pattern A) in embodiments 3 to 5;

[0080] FIGS. 28(b), (c) are sectional views of the noise filter of pattern B;

[0081]FIG. 28(d) is a diagram showing the relation of frequency and attenuation of noise filters of pattern A and pattern B in embodiments 3 to 5;

[0082]FIG. 29 is an equivalent circuit diagram of the noise filter of pattern B in a comparative example;

[0083]FIG. 30 is a perspective exploded view of common mode noise filter in embodiment 6 of the invention;

[0084]FIG. 31(a) is a sectional view of line A-A;

[0085]FIG. 31(b) is a perspective view thereof;

[0086] FIGS. 32(a) to (c) are perspective views showing the manufacturing method;

[0087] FIGS. 33(a) to (d) are perspective views showing the manufacturing method;

[0088]FIG. 34(a) is a diagram showing a waveform of carrier in a pair of signal lines in a cellular phone;

[0089]FIG. 34(b) is a diagram showing an example of the manner of use of the common mode noise filter in embodiment 6 of the invention;

[0090]FIG. 34(c) is a diagram showing the relation of frequency and attenuation amount when the common mode noise filter in embodiment 6 is used in a pair of signal lines in a cellular phone;

[0091]FIG. 35 is a perspective exploded view of a conventional noise filter; and

[0092]FIG. 36 is a perspective exploded view of a conventional common mode noise filter.

BEST MODE FOR CARRYING OUT THE INVENTION

[0093] (Embodiment 1)

[0094] A noise filter in embodiment 1 of the invention is explained by referring to the accompanying drawings.

[0095]FIG. 1 is a perspective exploded view of a noise filter in embodiment 1 of the invention, FIG. 2(a) is a sectional view along line A-A of the noise filter, and FIG. 2(b) is a perspective view of the noise filter.

[0096] Hereinafter, the first impedance element is supposed to be a first coil, the second impedance element to be a second coil, the first normal impedance element to be a first conductor, the first common impedance element to be a second conductor, the second common impedance element to be a third conductor, and the second normal impedance element to be a fourth conductor.

[0097] In FIG. 1 and FIG. 2, a first coil 21 is composed of a spiral first conductor 22 and a spiral second conductor 23 formed above the first conductor 22. The first conductor 22 includes a first leading-out portion 22 a and a first via electrode 22 b positioned in the center of the vortex, and the second conductor 23 includes a second leading-out portion 23 a and a second via electrode 23 b positioned in the center of the vortex. The first conductor 22 and second conductor 23 are formed so that, when a current flows in between the leading-out portions 22 a, 23 a, the current flowing in the first conductor 22 and second conductor 23 may be in the same direction (clockwise or counterclockwise) in a plan view as seen from above the second conductor 23. The leading-out portions 22 a, 23 a are formed at opposite positions to the mutually plane direction.

[0098] The square first magnetic sheet 24 is formed between the first conductor 22 and second conductor 23, and has a first via hole 24 a. A first via electrode 22 b and a second via electrode 23 b are mutually connected through the first via hole 24 a, and the first conductor 22 and second conductor 23 are connected, thereby forming the first coil 21.

[0099] A second coil 25 is composed of a spiral third conductor 26 and a spiral fourth conductor 27 formed above the third conductor 26. The third conductor 26 includes a third leading-out portion 26 a and a third via electrode 26 b positioned in the center of the vortex, and the fourth conductor 27 includes a fourth leading-out portion 27 a and a fourth via electrode 27 b positioned in the center of the vortex. The third conductor 26 and fourth conductor 27 are formed so that, when a current flows in between the leading-out portions 26 a, 27 a, the current flowing in the third conductor 26 and fourth conductor 27 may be in the same direction (clockwise or counterclockwise) in a plan view as seen from above the fourth conductor 27. The leading-out portions 26 a, 27 a are formed at opposite positions to the mutually plane direction, and in the same direction as the leading-out portions 26 a, 22 a.

[0100] The square second magnetic sheet 28 is formed between the third conductor 26 and fourth conductor 27, and has a second via hole 29. A third via electrode 26 b and a fourth via electrode 27 b are mutually connected through the second via hole 29, and the third conductor 26 and fourth conductor 27 are connected, thereby forming the second coil 25.

[0101] In FIG. 2(a), the first via hole 24 a and second via hole 29 are nearly the same position in a top view, but they may be located at mutually deviated positions in a top view.

[0102] The conductors 22, 23, 26, 27 are made of conductive material such as silver or copper, and their length, width and thickness may be adjusted to conform to the specified characteristics. By using copper, the baking process mentioned below can be omitted, or by using silver, baking can be done in air atmosphere. The spiral conductors 22, 23, 26, 27 are formed on a same plane. The overall dimensions (vertical and lateral dimensions excluding the leading-out portions 22 a, 23 a, 26 a, 27 a), conductor pitch, and number of turns are nearly equal. That is, excluding the leading-out portions 22 a, 23 a, 26 a, 27 a, the conductors 22, 23, 26, 27 are nearly identical in shape. However, the outward direction from the center of the first spiral conductor 22 and third spiral conductor 26 is counterclockwise in a plan view as seen from above the fourth conductor 27, whereas the second conductor 23 and fourth conductor 27 are clockwise.

[0103] Further, the second conductor 23 and third conductor 26 are opposite to each other, and are mutually insulated. When a current flows from the leading-out portions 22 a, 26 a drawn in the same direction into the leading-out portions 23 a, 27 a, they are formed so that the current may flow in the same direction (clockwise or counterclockwise) in the second conductor 23 and third conductor 26 in a plan view as seen from above the fourth conductor 27 (above the magnetic member 32 mentioned below).

[0104] By forming the conductors 22, 23, 26, 27 in such configuration, one end (second via electrode 23 b or third via electrode 26 b) of the second conductor 23 or third conductor 26 is connected individually in the vertical direction (the second conductor 23 to the first conductor 22 beneath, the third conductor 26 to the fourth conductor 27 above), so that there is no possibility of short-circuiting of the second conductor 23 and third conductor 26. Accordingly, unlike the conventional noise filter, the second conductor 23 and third conductor 26 can be extended by a necessary portion, and further the second conductor 23 and third conductor 26 are formed spirally, so that the overlapping region of the second conductor 23 and third conductor 26 can be increased. As a result, when the current flows in the same direction in the second conductor 23 and third conductor 26, the magnetic fluxes generated in the second conductor 23 and third conductor 26 can be mutually reinforced, so that the impedance value in the common mode can be heightened.

[0105] Further, if the current flows in reverse directions in the second conductor 23 and third conductor 26 and the magnetic fluxes generated in the second conductor 23 and third conductor 26 cancel with each other, since the first conductor 22 and fourth conductor 27 are formed at remote positions from the second conductor 23 and third conductor 26, the magnetic fluxes generated in the first conductor 22 and fourth conductor 27 do not cancel each other, and the impedance value in the normal mode can be enhanced.

[0106] The square third magnetic sheet 30 is formed between the first coil 21 and second coil 25 (between the second conductor 23 and third conductor 26). By the third magnetic sheet 30, the second conductor 23 and third conductor 26 are insulated from each other. The square fourth magnetic sheet 31 is formed on the lower surface of the first coil 21 (lower surface of the first conductor 22) and the upper surface of the second coil 25 (upper surface of the fourth conductor 27).

[0107] The magnetic sheets 24, 28, 30, 31 are composed of a mixture of ferrite powder oxide and resin, and a resin composite material mixing resin and ferrite, glass ceramic, or other derivatives may be used. When using the resin, the baking process can be skipped as described below. Besides, by laminating in the vertical direction, a square and flat magnetic member 32 is formed. The magnetic member 32 may also have a certain thickness, not being limited to be flat. The magnetic member 32 is not always required to be square. The thickness may be adjusted properly depending on the required characteristics (impedance, withstand voltage, etc.), and the thickness may be adjusted by varying the thickness of the magnetic sheet itself, or by changing the number of magnetic sheets to be formed.

[0108] The magnetic member 32 is impregnated with fluorine silane coupling agent, and the water-repellent fluorine silane coupling agent permeates into fine pores in the magnetic member 32, so that the humidity resistance of the noise filter can be enhanced.

[0109] Of the external electrodes 33 a, 33 b, 33 c, 33 d formed at both ends of the magnetic member 32, 33 a and 33 c are formed at one end of the magnetic member 32, and 33 b and 33 d are formed at other end of the magnetic member 32. The external electrodes 33 a, 33 b, 33 c, 33 d are plated with low melting metal such as nickel, tin or solder on the surface of the conductors of silver or the like.

[0110] The both ends of the first coil 21, that is, the first leading-out portion 22 a and second leading-out portion 23 a are electrically connected to the external electrode 33 a and external electrode 33 b, respectively.

[0111] Similarly, in the second coil 25, the third leading-out portion 26 a is electrically connected to the external electrode 33 c, and the fourth leading-out portion 27 a to the external electrode 33 d. That is, the first conductor 22 and third conductor 26 are drawn out to one end of the magnetic member 32, and the second conductor 23 and fourth conductor 27 are drawn out to the other end of the magnetic member 32.

[0112] By forming the second conductor 23 and third conductor 26 in a spiral shape, the conductor length can be extended, and the overlap region of the second conductor 23 and third conductor 26 can be increased. As a result, by passing the current in the second conductor 23 and third conductor 26 in a same direction, the impedance in the common mode can be further heightened.

[0113] At least the second conductor 23 and third conductor 26 are formed by electrocasting method, and a smaller conductor width and narrower conductor pitch can be realized, and the length of the spiral second conductor 23 and third spiral conductor 26 can be further extended. As a result, the overlap region of the second conductor 23 and third conductor 26 is much increased, and by passing the current in the second conductor and third conductor in the same direction, the magnetic fluxes generated in the second conductor and third conductor can further reinforce each other, and the impedance in the common mode become much higher.

[0114] On the other hand, when the conductors are formed by printing, the precision of the mask is limited, and smaller conductor width and narrower conductor pitch are not realized, and the impedance in the common mode can be increased only to a certain extent.

[0115] Further, when the second conductor 23 and third conductor 26 are spiral and the current flows from the external electrodes 33 a, 33 c drawn out in the same direction to the external electrodes 33 b, 33 d, in a plan view from above the magnetic member 32, the current flows in the same direction (clockwise or counterclockwise) in the second conductor 23 and third conductor 26, and the impedance in the common mode is heightened in such configuration. Accordingly, there is no problem if the first conductor 22 and fourth conductor 27 are deviated in position in a plan view from above the magnetic member 32, or different in the winding direction with respect to the second conductor 23 and third conductor 26. Not limited to a spiral shape formed on a plane, spiral lamination, arch or other shape may be possible. In the vortical or spiral shape, however, the generated magnetic flux is strong. For heightening the impedance in the normal mode, the spiral shape is preferred. In the case of a linear shape, the generated magnetic flux is weak and it is not suited to the purpose of the invention.

[0116]FIG. 3(a) is a diagram showing the impedance characteristic when normal mode and common mode current flows in the noise filter in embodiment 1 of the invention.

[0117] At this time, in each mode current, the frequency was varied, and the impedance between the input and output terminals was measured (the measuring circuit is shown in FIG. 3(b)). Samples were conductors 22, 23, 26, 27 measuring 600 μm×600 μm in overall dimensions (vertical and lateral dimensions excluding the leading-out portions 22 a, 23 a, 26 a, 27 a), with the number of turns of 4.

[0118] As clear from FIG. 3(a), the noise filter in embodiment 1 of the invention can heighten the impedance in both normal mode and common mode.

[0119] FIGS. 4(a) to (d) are top views of conductors 22, 23, 26, 27 of the noise filter in embodiment 1 of the invention.

[0120] If the first conductor 22 is replaced by the second conductor 23, the external electrodes 33 a and 33 b are formed at one end of the magnetic member 32, and the external electrodes 33 c and 33 d at other end. This pattern is called pattern B, and the pattern explained above is pattern A. The first conductor 22 and second conductor 23 are nearly identical in shape in a plan view as seen from above the magnetic member 32, except for the leading-out portions 22 a, 23 a, and therefore the characteristics are hardly changed (the sectional view at this time is shown in FIG. 4(e)).

[0121] The pattern A (embodiment 1 of the invention) is formed by laminating the first conductor 22, second conductor 23, third conductor 26, and fourth conductor 27 sequentially from the bottom, and pattern B is formed by laminating the second conductor 23, first conductor 22, third conductor 26, and fourth conductor 27 sequentially from the bottom.

[0122] Thus, if the vertical relation of the conductors 22, 23, 26, 27 is changed, their shapes are almost identical except for the leading-out portions 22 a, 23 a, 26 a, 27 a, and therefore it is not needed to inspect the vertical relation of the conductors 22, 23, 26, 27, so that the productivity may be enhanced.

[0123]FIG. 5(a) is an equivalent circuit diagram of the noise filter (pattern A) in embodiment 1 of the invention, and FIG. 5 (b) is an equivalent circuit diagram of the same noise filter (pattern B).

[0124]FIG. 6(a) is a diagram showing the impedance characteristics (attenuation characteristics) when a normal mode current is applied to the noise filter of pattern A and noise filter of pattern B in embodiment 1 of the invention.

[0125]FIG. 6(b) is a diagram showing the direction of current applied to each pattern, simulating pattern A and pattern B (pattern B1, pattern B2). Samples are same as in FIG. 3.

[0126] It is known from FIG. 6 that the attenuation characteristics vary depending on the direction of the applied current in the case of pattern B.

[0127] This is because, in the noise filter (pattern A) in embodiment 1 of the invention, the distance between the external electrodes 33 a, 33 c formed at one end of the magnetic member 32 and the vicinity of junction (leading-out portions 22 a, 26 a) of the first conductor 22 and third conductor 26, and the distance between the external electrodes 33 b, 33 d formed at other end of the magnetic member 32 and the vicinity of junction (leading-out portions 23 a, 27 a) of the second conductor 23 and fourth conductor 27 are equal to each other, and if the applied direction of the normal mode current is different, the floating capacity generated in the magnetic member is invariable, and therefore if the mounting direction on the substrate is different, the attenuation characteristics are not changed. It is hence not necessary to specify the mounting direction on the substrate, and the steps of marking the product direction and others can be omitted.

[0128] In the case of pattern B, on the other hand, the distance between the external electrodes 33 a, 33 d formed at one end of the magnetic member 32 and the vicinity of junction (leading-out portions 22 a, 27 a) of the first conductor 22 and fourth conductor 27, and the distance between the external electrodes 33 b, 33 c formed at other end of the magnetic member 32 and the vicinity of junction (leading-out portions 23 a, 26 a) of the second conductor 23 and third conductor 26 are different. Therefore, if the applied direction of the normal mode current is different, the distance between the vicinities of junction (leading-out portion) close to the input and output parts is different, and the floating capacity generated in the magnetic member varies, and the attenuation characteristics are changed, and it is necessary to mark the product direction.

[0129] However, in the case of pattern B (the first conductor 22 formed immediately beneath the third conductor 26), the first conductor 22 and third conductor 26 are nearly identical in shape except for the leading-out portions 22 a, 23 a, 26 a, 27 a, and the direction from the center of vortex to the outer side is counterclockwise in a plan view as seen from above the magnetic member 32, so that they are formed to overlap in a plan view as seen from above the magnetic member 32. At this time, each overlap area can be increased to a maximum extent, and the generated magnetic fluxes are mutually reinforced, and the impedance of the common mode can be increased to a maximum extent.

[0130] In this embodiment 1, the external electrodes 33 a to 33 d are formed at both ends of the magnetic member 32, but same effects are obtained if formed at four corners in a top view of the magnetic member 32.

[0131] In the noise filter of embodiment 1 of the invention having such configuration, its manufacturing method is explained below by referring to the accompanying drawings.

[0132] FIGS. 7(a) to (f) show the manufacturing method of the noise filtering embodiment 1 of the invention.

[0133] First, from a mixture of oxide of ferrite powder and resin, square first magnetic sheet 24, second magnetic sheet 28, third magnetic sheet 30, and fourth magnetic sheet 31 are fabricated.

[0134] At specified positions of the first magnetic sheet 24 and second magnetic sheet 28, a first via hole 24 a and a second via hole 29 are formed by laser, punching, or other drilling process. Preferably, when the via holes 24 a, 29 are filled with silver or other conductive material, the connection of the first conductor 22 and second conductor 23, and that of the third conductor 26 and fourth conductor 27 are achieved more securely.

[0135] Next, as shown in FIG. 7(a), a mask is formed on a base plate 33 so as to expose patterns of conductors 22, 23, 26, 27, and the exposed portion is plated with silver and the mask is removed (electrocasting method), so that a plurality of spiral first conductor 22, second conductor 23, third conductor 26, and fourth conductor 27 made of silver or the like can be manufactured.

[0136] The conductors 22, 23, 26, 27 have a first via electrode 22 b, a second via electrode 23 b, a third via electrode 26 b, and a fourth via electrode 27 b, respectively, positioned in the center of vortex at one end, and have a first leading-out portion 22 a, a second leading-out portion 23 a, a third leading-out portion 26 a, and a fourth leading-out portion 27 a at the other end.

[0137] The conductors 22, 23, 26, 27 are almost identical in shape except for the leading-out portions 22 a, 23 a, 26 a, 27 a. The leading-out portions 22 a, 23 a, and 26 a, 27 a are disposed at mutually confronting positions in the horizontal direction, so that the leading-out portion 26 a may face the same direction as the leading-out portion 22 a.

[0138] Further, a plurality of first conductors 22 are formed on the top of the specified number of fourth magnetic sheets 31, the first magnetic sheet 24 having the first via hole 24 a is provided on the top of the first conductors 22, and a plurality of second conductors 23 are provided on the top of the first magnetic sheets 24, thereby forming the first coil 21.

[0139] At this time, the first via electrode 22 b and second via electrode 23 b are connected through the first via hole 24 a, and the first conductor 22 and second conductor 23 are electrically connected.

[0140] The third magnetic sheet 30 is formed on the top of the second conductors 23.

[0141] A plurality of third conductors 26 are formed on the top of the third magnetic sheets 30, the second magnetic sheet 28 having the second via hole 29 is provided on the top of the third conductors 26, and a plurality of fourth conductors 27 are provided on the top of the second magnetic sheets 28, thereby forming the second coil 25.

[0142] At this time, the third via electrode 26 b and fourth via electrode 27 b are connected through the second via hole 29, and the third conductor 26 and fourth conductor 27 are electrically connected.

[0143] The laminating method of the conductors 22, 23, 26, 27 is not limited to the above sequence, and, for example, the magnetic sheets may be laminated with each other after once forming on the magnetic sheets 24, 28, 30, 31 formed beneath the conductors 22, 23, 26, 27.

[0144] A specified number of fourth magnetic sheets 31 are formed on the top of the fourth conductors 27, and laminated in the configuration as shown in FIG. 7(b).

[0145] As shown in FIG. 7(c), in one noise filter, the conductors 22, 23, 26, 27 are cut off and incorporated by one piece each, and one laminated body 34 is obtained as shown in FIG. 7(d). At this time, the first leading-out portion 22 a and third leading-out portion 26 a are exposed from both ends of the laminated body 34, and the second leading-out portion 23 a and fourth leading-out portion 27 a are exposed at other ends.

[0146] This laminated body 34 is baked, and a magnetic member 32 is formed.

[0147] The magnetic member 32 is chamfered as shown in FIG. 7(e).

[0148] Finally, as shown in FIG. 7(f), silver or other conductors are formed in the leading-out portions 22 a, 23 a, 26 a, 27 a exposed at both ends of the magnetic member 32, and their surfaces are plated with low melting metal such as nickel, tin or solder. As a result, the external electrode 33 a is formed in the first leading-out portion 22 a, external electrode 33 b is formed in the second leading-out portion 23 a, external electrode 33 c is formed in the third leading-out portion 26 a, and external electrode 33 d is formed in the fourth leading-out portion 27 a, so that the noise filter in embodiment 1 of the invention is manufactured.

[0149] After forming silver or other conductors, and before nickel plating, the magnetic member 32 is impregnated in fluorine silane coupling agent in decompressed atmosphere.

[0150] In the noise filter in embodiment 1 of the invention, by shortening the distance between the second conductor 23 and third conductor 26 to have a large magnetic coupling, the impedance in common mode can be heightened, but if the distance between the second conductor 23 and third conductor 26 is too close, the withstand voltage between the second conductor 23 and third conductor 26 is impaired, and the second conductor 23 and third conductor 26 may be short-circuited.

[0151] Therefore the distance between the second conductor 23 and third conductor 26 (the thickness of the third magnetic sheet 30) should be specified within a specific range.

[0152]FIG. 8 is a diagram showing the relation of the distance, coupling coefficient, and withstand voltage between the second conductor 23 and third conductor 26 of the noise filter in embodiment 1 of the invention.

[0153] The withstand voltage is tested by applying a voltage of 100 V between the second conductor 23 and third conductor 26 for 1 minute, and the rate of conforming samples (insulation resistance 108 ohms or more) is expressed, and the axis of abscissas denotes the distance between the second conductor 23 and third conductor 26, and the axis of ordinates represents the coupling coefficient and withstand voltage defective percentage. Samples are conductors 22, 23, 26, 27 measuring 600 μm×600 μm in overall dimensions, with number of turns of 4.

[0154] As clear from FIG. 8, the distance between the second conductor 23 and third conductor 26 should be 50 microns or longer and 200 microns or shorter. Thus, the withstand voltage between the second conductor 23 and third conductor 26 is maintained, and the coupling coefficient between the second conductor 23 and third conductor 26 is enhanced, so that the impedance in common mode becomes higher.

[0155] The noise filter of this type generally measures 1.0 mm×1.0 mm×0.5 mm thick, and the vertical and lateral overall dimensions of the conductors 22, 23, 26, 27 are usually 500 μm to 800 μm, and therefore in relation to the vertical and lateral overall dimensions of the conductors 22, 23, 26, 27, the distance between the second conductor 23 and third conductor 26 is ¼ to {fraction (1/16)}.

[0156] In these conditions, a magnetic coupling coefficient of 0.2 to 0.7 is obtained as clear from FIG. 8. Fluctuations of the coupling coefficient are due to change in the distance between the second conductor 23 and third conductor 26 (when the conditions of the material of the magnetic member 32 and others are equal).

[0157] Further, the coupling coefficient also varies with the number of turns of the conductors 22, 23, 26, 27. For example, when the number of turns of the first conductor 22 and fourth conductor 27 is 1, and the number of turns of the second conductor 23 and third conductor 26 is 6, the coupling coefficient is 0.5 to 0.95. It is not realistic to have the difference in the number of turns by 6 times or more, in embodiment 1 of the invention, the coupling coefficient of the noise filter is 0.2 to 0.95. Hence, the impedance can be heightened in both common mode and normal mode.

[0158] Thus, by varying the distance between the second conductor 23 and third conductor 26 and the number of turns of each conductor, the coupling coefficient can be controlled to a desired value.

[0159] Or, as shown in FIG. 9, by setting in the relation of T1, T2>t, where T1 is the distance between the first conductor 22 and second conductor 23, T2 is the distance between the third conductor 26 and fourth conductor 27, and t is the distance between the second conductor 23 and third conductor 26, the floating capacity generated between the first conductor and second conductor, between the third conductor and fourth conductor, and between the first conductor and fourth conductor can be decreased. As a result, the impedance value elevates in the high frequency region, and the distance between the first and fourth conductors can be extended, and the magnetic fluxes generated in the first and fourth conductors do not cancel each other, so that the impedance in normal mode becomes higher.

[0160]FIG. 10 is a diagram of frequency characteristic showing improvement of impedance value in the high frequency region.

[0161] In FIG. 10, frequency characteristic C shows the case in which the distance between the first conductor 22 and second conductor 23, and between the third conductor 26 and fourth conductor 27 is nearly same as the distance between the second conductor 23 and third conductor 26, and, as shown in FIG. 9, frequency characteristic D shows the case in which the distance between the first conductor 22 and second conductor 23, and between the third conductor 26 and fourth conductor 27 is longer than the distance between the second conductor 23 and third conductor 26, and the axis of ordinates represents the impedance, and the axis of abscissas shows the frequency of applied current.

[0162] As clear from FIG. 10, the frequency showing the peak impedance is higher in D than in C. That is, characteristic D has the noise removing property of higher frequency.

[0163] In the noise filter in embodiment 1 of the invention, other examples for enhancing the impedance in high frequency region are explained, but the frequency changing rate varies with each condition.

[0164] Further, as shown in FIGS. 11(a) and (b), when a material 34 a lower in permeability than the magnetic member 32 is disposed between the first conductor 22 and second conductor 23, and between the third conductor 26 and fourth conductor 27, the magnetic fluxes generated in the first conductor 22 and fourth conductor 27 do not cancel each other, so that the impedance in normal mode becomes higher.

[0165] As the material 34 a lower in permeability, a non-magnetic material may be disposed between the first magnetic sheet 24 and second magnetic sheet 28, or part or whole of the first magnetic sheet 24 and second magnetic sheet 28 may be made of non-magnetic material, or the permeability may be lowered by changing the composition of the magnetic material.

[0166] However, instead of forming a material 34 a of low permeability in all between the first conductor 22 and second conductor 23, and between the third conductor 26 and fourth conductor 27 as shown in FIG. 11(a), it is more preferable to compose as shown in FIG. 11(b) in which at least a material 34 a low in permeability is used together with the material (magnetic member 32) of high permeability disposed between the second conductor 23 and third conductor 26, because the impedance in common mode is higher. This is because the magnetic fluxes generated in the second conductor 23 and third conductor 26 are stronger by forming a material of high permeability between the two.

[0167] As shown in FIGS. 12(a) to (d), by setting the conductor length equal between external electrodes in the first and second coils 21, 25, since the total coil length including the leading-out portions 22 a, 23 a, 26 a, 27 a is equal, the impedance values in the first and second coils 21, 25 are equal.

[0168] As its means, the conductors 22, 23, 26, 27 are formed symmetrically to the line 35 passing through the via electrodes 22 b, 23 b, 26 b, 27 b of the conductors. Point 36 is the intersection of the conductors 22, 23, 26, 27 with the line 35. Moreover, the portions 37 of the leading-out portions 22 a, 23, 26 a, 27 a exposed to the end of the magnetic member 32 are formed symmetrically to the line 35. Between the points 36 and 37, the length of the leading-out portions 22 a, 23 a, 26 a, 27 a should be equalized.

[0169] Further, as shown in FIG. 13, between the second conductor 23 and third conductor 26, when the density is set higher than in other parts, the porosity between the second conductor 23 and third conductor 26 can be lowered, so that the withstand voltage between the second conductor 23 and third conductor 26 can be assured.

[0170] At this time, a fifth magnetic sheet 38 of higher density than other magnetic sheet (magnetic member 32) in the portion between the second conductor 23 and third conductor 26 may be provided, and as the material for the fifth magnetic sheet 38, the content of sintering aid such as CuO or Bi2O3 may be increased, or the fifth magnetic sheet 38 of higher density than other magnetic sheet (magnetic member 32) may be used.

[0171] (Embodiment 2)

[0172] A noise filter in embodiment 2 of the invention is explained by referring to the drawings.

[0173] The noise filter in embodiment 2 of the invention differs from embodiment 1 of the invention only in that the first conductor 22 c and second conductor 23 c, and the third conductor 26 c and fourth conductor 27 c are formed so as not to overlap in a plan view as seen from above the magnetic member 32, and other structure and manufacturing method are same and are not explained herein.

[0174] FIGS. 14(a), (b), (d), and (e) are top views of the conductors 22 c, 23 c, 26 c, 27 c of the noise filter in embodiment 2 of the invention, and FIGS. 14(c) and (f) are pattern see-through diagrams of the first conductor 22 c and second conductor 23 c, and the third conductor 26 c and fourth conductor 27 c of the noise filter, respectively.

[0175] In FIG. 14, the first conductor 22 c and second conductor 23 c, and the third conductor 26 c and fourth conductor 27 c are orthogonal respectively, and they are formed so as not to overlap except for the orthogonal parts in a plan view as seen from above the magnetic member 32. As a result, the floating capacity generated between the first conductor 22 c and second conductor 23 c, and between the third conductor 26 c and fourth conductor 27 c can be decreased, and hence the impedance value is elevated in the high frequency region.

[0176] Alternatively, the first conductor 22 c and fourth conductor 27 c may be formed so as not to overlap with the second conductor 23 c and third conductor 26 c in a plan view as seen from above the magnetic member 32.

[0177] The second conductor 23 c and third conductor 26 c are formed so that, when a current flows in the leading-out portions 23 a, 27 a (external electrodes 33 b, 33 d) from the leading-out portions 22 a, 26 a (external electrodes 33 a, 33 c) drawn out in the same direction, the current may flow in the same direction (clockwise or counterclockwise) in a plan view as seen from above the magnetic member 32.

[0178] In the noise filter in embodiments 1 and 2 of the invention, two coils 21 and 25 (impedance elements) are stacked up, but same effects are obtained by stacking up in plural layers.

[0179] In this case, the conductors adjacent in the vertical direction (common impedance elements) can heighten the impedance value in common mode, and the conductors in the highest position and lowest position (normal impedance elements) can heighten the impedance value in normal mode, and the conductors between the common impedance element and normal impedance element have an intermediate value of the normal mode impedance and common mode impedance.

[0180] In this way, the impedance values in both normal mode and common mode, and the coupling coefficient expressing the degree of coupling of coils can be easily adjusted and designed to desired values. Herein, when the coupling coefficient is large, the impedance value in common mode becomes large.

[0181] The method of using the noise filter in embodiments 1 and 2 of the invention in a pair of signal lines in the cellular phone or other wireless communication appliance is explained.

[0182] For example, signal lines of communication wires in the headset of a cellular phone are usually composed of a pair of cables (signal lines), and since the high frequency signal such as carrier of the cellular phone is superposed as radiation noise on the cables in normal mode and common mode, the effect of noise is likely to occur. For example, this radiation noise may occur as noise in the audio signal.

[0183] The audio signal is disturbed by the high frequency noise in common mode because the low frequency component in the signal is detected and superposed by the nonlinear element and electrostatic capacity in the circuit.

[0184] For example, as shown in FIG. 15(a), when carrier 900 MHz (TDMA carrier) in transmission and reception circuits of a cellular phone of TDMA system is transmitted and received at 217 Hz (burst frequency), 217 Hz is detected, and is superposed on the audio signal of normal mode, and audible noise may be heard. Therefore, if the current in common mode and normal mode to be induced can be suppressed, noise in audio output can be reduced.

[0185] As shown in FIG. 15(b), when the noise filters of embodiments 1, 2 of the invention were connected to a pair of signal lines (audio lines), the attenuation characteristics as shown in FIG. 15(c) were obtained.

[0186] As clear from FIG. 15(c), also by the carrier 900 MHz of the cellular phone, noise can be attenuated in both common mode and normal mode. Therefore, the signal of repetitive frequency 217 Hz detected together with the carrier 900 MHz can be reduced, so that the audible noise may not be heard.

[0187] In this way, when the noise filters in embodiments 1 and 2 of the invention are connected in a pair of signal lines in the cellular phone or wireless communication appliance, respectively to the first coil 21 (first impedance element) and second coil 25 (second impedance element), in the pair of signal lines in which noises in both common mode and normal mode are applied, impedances in both common mode and normal mode can be heightened (signals can be attenuated), so that the audible noise can be reduced in audio lines such as a pair of signal lines.

[0188] (Embodiment 3)

[0189] A noise filter in embodiment 3 of the invention is explained below by referring to the drawings.

[0190]FIG. 16 is a perspective exploded view of the noise filter in embodiment 3 of the invention, FIG. 17(a) is a sectional view of line A-A of the noise filter, and FIG. 17(b) is a perspective view of the noise filter.

[0191] In FIG. 16 and FIG. 17, a spiral first coil 121 is formed by laminating and connecting first inner conductors 121 a to 121 f sequentially from the bottom. A spiral second coil 122 is formed by laminating and connecting second inner conductors 122 a to 122 f sequentially from the bottom. That is, the first and second coils 121, 122 are composed of six layers each. However, the first and second coils 121, 122 are not required to be composed of six layers. The first inner conductors 121 a to 121 f, and second inner conductors 122 a to 122 f are made of silver or other conductive material.

[0192] The first inner conductors 121 a to 121 f, and second inner conductors 122 a to 122 f are formed in U-shape except for the lowest and highest layers thereof 121 a, 121 f, 122 a, 122 f. Not limited to U-shape, however, they may be formed in L- or other shape.

[0193] At this time, from the bottom sequentially, the first inner conductors 121 a to 121 c, second inner conductor 122 a, first inner conductor 121 d, second inner conductor 122 b, first inner conductor 121 e, second inner conductor 122 c, first inner conductor 121 f, and second inner conductors 122 d to 122 f are formed, and the portion composed of the first inner conductors 121 to 121 c only is a first laminated body 123, the portion composed alternately of the first inner conductors and second inner conductors (the portion forming the second inner conductor 122 a, first inner conductor 121 d, second inner conductor 122 b, first inner conductor 121 e, second inner conductor 122 c, and first inner conductor 121 f) is a second laminated body 124, and the portion composed of the second inner conductors 122 d to 122 f only is a third laminated body 125. That is, of the six-layer first and second coils 121, 122, three layers are formed alternately.

[0194] Of the first inner conductors 121 a to 121 f, in the lowest layer and highest layer 121 a, 121 f, first and second leading-out electrodes 126, 127 are formed as the ends of the first coil 121. Similarly, in the second inner conductors 122 a, 122 f, third and fourth leading-out electrodes 128, 129 are formed.

[0195] The leading-out electrodes 126, 127, 128, 129 may be also formed at four corners of the magnetic member 138 in a top view of the second inner conductor 122 f (magnetic member 138 described below).

[0196] A plurality of square first magnetic sheets 130 are formed beneath the first inner conductors 121 b, 121 c in the first laminated body 123, and a first via hole 131 is formed. Through this first via hole 131, the first inner conductors 121 a to 121 c are connected.

[0197] A plurality of square second magnetic sheets 132 are formed beneath the second inner conductors 122 d to 122 f in the third laminated body 125, and a second via hole 133 is formed. Through this second via hole 133, the second inner conductors 122 d to 122 f are connected.

[0198] A plurality of square third magnetic sheets 134 are formed beneath the second inner conductor 122 a, first inner conductor 121 d, second inner conductor 122 b, first inner conductor 121 e, second inner conductor 122 c, and first inner conductor 121 f forming the second laminated body 124, and a third via hole 135 and a fourth via hole 136 are formed (only the third via hole 135 is provided in the third magnetic sheet 134 formed beneath the second inner conductor 122 a).

[0199] The first inner conductors 121 c and 121 d, 121 d and 121 e, and 121 e and 121 f are connected through the third via hole 135, respectively, and the second inner conductors 122 a and 122 b, 122 b and 122 c, and 122 c and 122 d are connected through the four via hole 136, respectively.

[0200] That is, the fourth via hole 136 is formed in the third magnetic sheet 134 having the third via hole 135 beneath the first inner conductor 121 d. The first inner conductor 121 d is connected to the first inner conductor 121 c through this third via hole 135 and a third via hole 135 provided in the third magnetic sheet 134 formed further beneath (above the first inner conductor 121 c), and the second inner conductor 122 b is connected to the second inner conductor 122 a through this fourth via hole 136 and a fourth via hole 136 provided in the third magnetic sheet 134 formed further above (beneath the second inner conductor 122 b).

[0201] The third via hole 135 and second inner conductors 122 a to 122 c, and the fourth via hole 136 and first inner conductors 121 d to 121 f are electrically insulated from each other.

[0202] A plurality of square fourth magnetic sheets 137 are formed by a specific number each beneath the first inner conductor 121 a and above the second inner conductor 122 f.

[0203] Magnetic sheets 130, 132, 134, 137 are composed of a mixture of oxide of ferrite powder and resin, and a flat square magnetic member 138 is formed by laminating them in the vertical direction as described above. The magnetic member 138 may also have a certain thickness, not being limited to be flat. The magnetic member 138 is not always required to be square. The thickness may be adjusted properly depending on the required characteristics (impedance, withstand voltage, etc.), and the thickness may be adjusted by varying the thickness of the magnetic sheet itself, or by changing the number of magnetic sheets to be formed.

[0204] The magnetic member 138 is impregnated with fluorine silane coupling agent, and the water-repellent fluorine silane coupling agent permeates into fine pores in the magnetic member 138, so that the humidity resistance of the noise filter can be enhanced.

[0205] Of the external electrodes 139 a, 139 b, 139 c, 139 d formed at both ends of the magnetic member 138, 139 a and 139 c are formed at one end of the magnetic member 138, and 139 b and 139 d are formed at other end of the magnetic member 138. The external electrodes 139 a, 139 b, 139 c, 139 d are plated with low melting metal such as nickel, tin or solder on the surface of silver or other conductors.

[0206] The external electrodes 139 a, 139 b, 139 c, 139 d may be also formed at four corners of the magnetic member 138 in a top view of the magnetic member 138.

[0207] Both ends of the first coil 121, that is, the first leading-out portion 126 and second leading-out portion 127 are electrically connected to the external electrode 139 a and external electrode 139 b, respectively.

[0208] Similarly, in the second coil 122, the third leading-out portion 128 is electrically connected to the external electrode 139 c, and the fourth leading-out portion 129 to the external electrode 139 d.

[0209] As described herein, the noise filter in embodiment 3 of the invention has a three-layer structure consisting of the first laminated body 123 composed of the first inner conductors 121 a to 121 c only, the second laminated body 124 alternately laminating the first inner conductors 121 d, 121 e, 121 f and second inner conductors 122 a, 122 b, 122 c, being formed on the top of the first laminated body 123, and a third laminated body 125 composed of the second inner conductors 122 d to 122 f only, being formed on the top of the second laminated body 124. Accordingly, when the current flows in a same direction in the first coil 121 and second coil 122 (clockwise or counterclockwise in a top view of the magnetic member 138), since the first inner conductors 121 d, 121 e, 121 f and second inner conductors 122 a, 122 b, 122 c of the second laminated body 124 are formed alternately, the distance is closer between the alternately formed first inner conductors 121 d, 121 e, 121 f and second inner conductors 122 a, 122 b, 122 c, so that the magnetic fluxes generated in the first inner conductors 121 d, 121 e, 121 f and second inner conductors 122 a, 122 b, 122 c in the second laminated body 124 may reinforce each other. As a result, the impedance in common mode is higher, and if current flows in reverse directions in the first coil 121 and second coil 122, since only the first inner conductors 121 a to 121 c are formed in the first laminated body 123 and only the second inner conductors 122 d to 122 f are formed in the third laminated body 125, the magnetic fluxes generated in the first inner conductors 121 a to 121 c formed in the first laminated body 123 and in the second inner conductors 122 d to 122 f formed in the third laminated body 125 do not cancel each other, so that the impedance in normal mode may be enhanced.

[0210] Therefore, if a current flows in a same direction in the first coil 121 and second coil 122 (first inner conductors 121 d, 121 e, 121 f and second inner conductors 122 a, 122 b, 122 c in the second laminated body 124), the impedance in the first inner conductors 121 d, 121 e, 121 f and second inner conductors 122 a, 122 b, 122 c becomes high, and these inner conductors decrease the noise of the common mode. On the other hand, when flowing in opposite directions, the impedance becomes high in the first inner conductors 121 a to 121 c formed in the first laminated body 123 and the second inner conductors 122 d to 122 f formed in the third laminated body 125, and these inner conductors decrease the noise in normal mode.

[0211] That is, since the impedance can be heightened in both common mode and normal mode, the impedance of the common mode and normal mode can be adjusted to specified values individually.

[0212]FIG. 18 is an equivalent circuit diagram of the noise filter in embodiment 3 of the invention.

[0213] Incidentally, when the number of first inner conductors formed in the first laminated body 123 and the number of second inner conductors formed in third laminated body 125 are different, if a current flows in reverse directions in the first coil 121 and second coil 122, the intensity of magnetic fluxes generated in the first inner conductors formed in the first laminated body 123 and the second inner conductors formed in the third laminated body 125 is different, so that the impedance in normal mode entered from the first inner conductors may be set different from the impedance in normal mode entered from the second inner conductors.

[0214] It is also effective to adjust the magnetic coupling coefficient finely.

[0215] That is, in this noise filter, the first and second coils 121, 122 are individually composed of six layers, and three layers thereof, that is, half layers are formed alternately, but by varying the rate of the alternately formed portions (the rate of the inner conductors formed in the second laminated body 24 of the whole inner conductors), the rate of inner conductors capable of mutually reinforcing the generated magnetic fluxes is changed, so that the coupling coefficient changes.

[0216] When the coupling coefficient can be thus finely adjusted, the impedance in common mode and impedance in normal mode can be controlled to specified values, and this effect is outstanding.

[0217] Further, by maximizing or minimizing the rate of portions formed alternately, the coupling coefficient can be adjusted to a specified value between 0.2 to 0.95, and the impedance in normal mode and common mode can be adjusted.

[0218] In the noise filter in embodiment 3 of the invention, FIG. 19(a) is a diagram showing the relation of the number of turns (the number of turns of the first inner conductors 121 d to 121 f and second inner conductors 122 a to 122 c) and coupling coefficient of internal conductors in the second laminated body 124, and FIG. 19(b) is a diagram showing the relation of the number of turns (the number of turns of the first inner conductors 121 a to 121 c and second inner conductors 122 d to 122 f) and coupling coefficient of internal conductors in the first laminated body 123 and third laminated body 125. Herein, one turn is counted when the inner conductor makes one turn in a top view of the magnetic member 138. That is, when the inner conductor makes a 1/4 turn, four layers are laminated to make one turn.

[0219] Samples are magnetic members measuring 1.0 mm×1.0 mm×2.5 mm thick, with the portion surrounded by the spiral first coil 121 and second coil 122 measuring 600 μm×600 μm in a top view of the magnetic member. In FIG. 19(a), the number of turns of the inner conductors is 1 in the first laminated body 123 and third laminated body 125, and in FIG. 19(b), the number of turns of the inner conductors is 10 in the second laminated body 124.

[0220] As clear from FIGS. 19(a), (b), the coupling coefficient is larger as the number of turns of the inner conductors in the second laminated body 124 is larger, the number of turns of the inner conductors in the first laminated body and third laminated body is smaller, and the thickness of the magnetic sheets 130, 132, 134 is thinner.

[0221] The coupling coefficient is 0.2 to 0.95 when the number of turns of the inner conductors in the second laminated body 124 is 10 or less and the number of turns of the inner conductors in the first laminated body and third laminated body is 5 or more in the case of the thickness of the magnetic sheets 130, 132, 134 of 50 microns, and when the number of turns of the inner conductors in the second laminated body 124 is 5 to 11 and the number of turns of the inner conductors in the first laminated body and third laminated body is 4 or less in the case of the thickness of the magnetic sheets 130, 132, 134 of 100 μm.

[0222] As far as possible, meanwhile, when the number of turns of the inner conductors in the first laminated body and third laminated body is smaller and the number of turns of the inner conductors in the second laminated body 124 is larger, the coupling coefficient will be 0.95. Or, as far as possible, when the number of turns of the inner conductors in the first laminated body and third laminated body is larger and the number of turns of the inner conductors in the second laminated body 124 is smaller, the coupling coefficient will be 02.

[0223] Further, if the specified impedance in normal mode is obtained, the shape of the first inner conductors 121 a to 121 c formed in the first laminated body 123, and the shape of the second inner conductors 122 d to 122 f formed in the third laminated body 125 may not be limited, including the spiral, meandering or other shape formed on one plane. There is no problem if winding direction is reverse.

[0224] Incidentally, by bringing the first inner conductors 121 d, 121 e, 121 f and second inner conductors 122 a, 122 b, 122 c in the second laminated body 124 as close-to one turn as possible, the length of each inner conductor may be extended to a maximum extent, and therefore the magnetic fluxes generated in the first inner conductors 121 d, 121 e, 121 f, and the second inner conductors 122 a, 122 b, 122 c can reinforce each other, and if a current flows in a same direction in the first coil 121 and second coil 122 (the first inner conductors 121 d, 121 e, 121 f, and the second inner conductors 122 a, 122 b, 122 c in the second laminated body 124), the impedance in common mode can be further enhanced.

[0225] In the noise filter in embodiment 3 of the invention having such configuration, the manufacturing method is explained below by referring to the accompanying drawings.

[0226] FIGS. 20(a) to (g) are perspective views showing the manufacturing method of noise filter in embodiment 3 of the invention.

[0227] First, from a mixture of oxide of ferrite powder and resin, square first magnetic sheet 130, second magnetic sheet 132, third magnetic sheet 134, and fourth magnetic sheet 137 are fabricated.

[0228] Next, as shown in FIG. 20(a), a second via hole 133 is provided at a specified position of the second magnetic sheet 132 by laser, punching or other drilling process.

[0229] Further, as shown in FIG. 20(b), the second inner conductor 122 f having the fourth leading-out electrode 129 is formed by printing on the second magnetic sheet 132. At the same time, the second via hole 133 is filled with silver or other conductive material. At this time, the end of the second inner conductor 122 f is connected to the second via hole 133.

[0230] Same as in FIGS. 20(a), (b), the second inner conductors 122 d, 122 e are formed on the top of the second magnetic sheet 132 having the second via hole 133, the first inner conductors 121 d, 121 e, 121 f and second inner conductors 122 a, 122 b, 122 c are formed on the top of the third magnetic sheet 134 having the third via hole 135 and fourth via hole 136, and the first inner conductors 121 a, 121 b, 121 c are formed on the top of the first magnetic sheet 130 having the first via hole 131.

[0231] The inner conductors may be formed not only by printing, but also by other method such as plating, vapor deposition or sputtering.

[0232] Consequently, laminating in the configuration as shown in FIG. 20(c), spiral first and second coils 121, 122 are provided, and the first laminated body 123 composed of the first inner conductors 121 a to 121 c only, the second laminated body 124 formed on the top of the first laminated body 123 composed of the first inner conductors 121 d, 121 e, 121 f and second inner conductors 122 a, 122 b, 122 c alternately, and the third laminated body 125 formed on the top of the second laminated body 124 composed of the second inner conductors 122 d to 122 f only are formed.

[0233] As shown in FIG. 20(d), by cutting so that the first coil 121 and second coil 122 may be incorporated by one each in one noise filter, one laminated body 140 as shown in FIG. 20(e) is obtained. At this time, the first leading-out electrode 126 and third leading-out electrode 128 are exposed from both ends of the laminated body 140, and the second leading-out electrode 127 and fourth leading-out electrode 129 are exposed at other ends.

[0234] This laminated body 140 is baked, and a magnetic member 138 is formed.

[0235] The magnetic member 138 is chamfered as shown in FIG. 20(f).

[0236] Finally, as shown in FIG. 20(g), silver or other conductors are formed in the leading-out electrodes 126, 127, 128, 129 exposed at both ends of the magnetic member 138, and their surfaces are plated with low melting metal such as nickel, tin or solder, and the external electrode 139 a is formed in the first leading-out electrode 126, external electrode 139 b is formed in the second leading-out electrode 127, external electrode 139 c is formed in the third leading-out electrode 128, and external electrode 139 d is formed in the fourth leading-out electrode 129, and the noise filter in embodiment 3 of the invention is manufactured.

[0237] After forming silver or other conductors, and before nickel plating, the magnetic member 138 is impregnated in fluorine silane coupling agent in decompressed atmosphere.

[0238] Herein, by setting the interval of the adjacent first inner conductors 121 a to 121 c and second inner conductors 122 d to 122 f in the first laminated body 123 and third laminated body 125 larger than the interval of the adjacent first inner conductors 121 d to 121 f and second inner conductors 122 a to 122 c in the second laminated body 124, it is effective to decrease the floating capacity generated in the adjacent first inner conductors 121 a to 121 c and second inner conductors 122 d to 122 f in the first laminated body 123 and third laminated body 125, and in the first inner conductors 121 a to 121 c in the first laminated body 123 and the second inner conductors 122 d to 122 f in the third laminated body 125. Accordingly, the impedance is enhanced in the high frequency region, and the distance between the first inner conductors 121 a to 121 c in the first laminated body 123 and the second inner conductors 122 d to 122 f in the third laminated body 125 can be extended. Therefore, the magnetic fluxes generated in the first inner conductors 121 a to 121 c in the first laminated body 123 and the second inner conductors 122 d to 122 f in the third laminated body 125 do not cancel each other, and the impedance in normal mode is enhanced.

[0239] Further, by forming a sheet of a lower permeability than that of the magnetic member 138 between the adjacent first inner conductors 121 a to 121 c and second inner conductors 122 d to 122 f in the first laminated body 123 and third laminated body 125, the magnetic fluxes generated in the first inner conductors 121 a to 121 c in the first laminated body 123 and the second inner conductors 122 d to 122 f in the third laminated body 125 can be weakened, so that the impedance in normal mode can be lowered. Therefore, when the impedance in common mode is constant, by controlling the impedance in normal mode, the coupling coefficient can be adjusted.

[0240] Also by equalizing the length among the external electrodes in the first and second coils 121, 122 (between 139 a and 139 b, and 139 c and 139 d), the total coil length including the leading-out portions is equal, so that the impedance values may be same in the first and second coils 121, 122.

[0241] Moreover, by setting the density of the magnetic member in the first coil 121 (first inner conductors 121 d to 121 f) and second coil 122 (second inner conductors 122 a to 122 c) in the second laminated body 124 higher than that of the magnetic member in other parts (first laminated body 123, third laminated body 125), it is effective to lower the porosity between the first coil 121 and second coil 122 (between the first inner conductors 121 d to 121 f and second inner conductors 122 a to 122 c in the second laminated body 124), so that the withstand voltage between the first inner conductors 121 d to 121 f and second inner conductors 122 a to 122 c in the second laminated body 124 may be maintained.

[0242] (Embodiment 4)

[0243] A noise filter in embodiment 4 of the invention is explained by referring to the drawings.

[0244]FIG. 21 is a perspective view of the noise filter in embodiment 4 of the invention. In FIG. 21, a spiral first coil 141 is formed by laminating and connecting first inner conductors 141 a to 141 i sequentially from the bottom. Reference numeral 142 is a spiral second coil, which is formed by laminating and connecting second inner conductors 142 a to 142 i sequentially from the bottom. That is, the first and second coils 141, 142 are composed of nine layers. The first and second coils 141, 142 are not required to have nine-layer structure. The first inner conductors 141 a to 141 i and second inner conductors 142 a to 142 i are made of silver or other conductive material.

[0245] The first inner conductors 141 a to 141 i and second inner conductors 142 a to 142 i are formed in U-shape except for the lowest and highest layers thereof 141 a, 141 i, 142 a, 142 i. Not limited to U-shape, however, they may be formed in L- or other shape.

[0246] More specifically, the first inner conductors 141 a to 141 d, first inner conductor 141 e and second inner conductor 142 a formed on a same plane, first inner conductor 141 f and second inner conductor 142 b formed on a same plane, first inner conductor 141 g and second inner conductor 142 c formed on a same plane, first inner conductor 141 h and second inner conductor 142 d formed on a same plane, first inner conductor 141 i and second inner conductor 142 e formed on a same plane, and second inner conductors 142 f to 142 i are formed sequentially from the bottom, and a portion composed of first inner conductors 141 a to 141 d only forms a first laminated body 143, a portion composed of first inner conductor and second inner conductor on a same plane (each portion forming the first inner conductor 141 e and second inner conductor 142 a, first inner conductor 141 f and second inner conductor 142 b, first inner conductor 141 g and second inner conductor 142 c, first inner conductor 141 h and second inner conductor 142 d, and first inner conductor 141 i and second inner conductor 142 e) forms a second laminated body 144, and a portion composed of second inner conductors 142 f to 142 i only forms a third laminated body 145. That is, of the nine layers of the first and second coils 141, 142, five layers are formed on a same plane.

[0247] In the lowest and highest layers 141 a, 141 i of the first inner conductors 141 a to 141 i, first and second leading-out electrodes 146, 147 are formed as the ends of the first coil 141. Similarly, third and fourth leading-out electrodes 148, 149 are formed in the second inner conductors 142 a, 142 i.

[0248] The leading-out electrodes 146, 147, 148, 149 may be also formed at four corners of the magnetic member 158 in a top view of the second inner conductor 142 i (magnetic member 158 described below).

[0249] A plurality of square first magnetic sheets 150 are formed beneath the first inner conductors 141 b to 141 d in the first laminated body 143, and a first via hole 151 is formed. Through this first via hole 151, the first inner conductors 141 a to 141 d are connected.

[0250] A plurality of square second magnetic sheets 152 are formed beneath the second inner conductors 142 f to 142 i in the third laminated body 145, and a second via hole 153 is formed. Through this second via hole 153, the second inner conductors 142 e to 142 i are connected.

[0251] A plurality of square third magnetic sheets 154 are formed beneath the first inner conductor 141 e and second inner conductor 142 a, first inner conductor 141 f and second inner conductor 142 b, first inner conductor 141 g and second inner conductor 142 c, first inner conductor 141 h and second inner conductor 142 d, and first inner conductor 141 i and second inner conductor 142 e formed respectively on a same plane of the second laminated body 144, and a third via hole 155 and a fourth via hole 156 are formed (only the third via hole 155 is provided in the magnetic sheet 154 formed beneath the first inner conductor 141 e and second inner conductor 142 a formed on a same plane).

[0252] The first inner conductors 141 e and 141 f, 141 f and 141 g, 141 g and 141 h, and 141 h and 141 i are connected through the third via hole 155, respectively. The second inner conductors 142 a and 142 b, 142 b and 142 c, 142 c and 142 d, and 142 d and 142 e are connected through the four via hole 156, respectively.

[0253] That is, the fourth via hole 156 is formed in the third magnetic sheet 154 having the third via hole 155 beneath the first inner conductor 141 f. The first inner conductor 141 f is connected to the first inner conductor 141 e through this third via hole 155, and the second inner conductor 142 b formed on the same plane as the first inner conductor 141 f is connected to the second inner conductor 142 a through this fourth via hole 156.

[0254] The first inner conductor and second inner conductor formed on a same plane are electrically insulated from each other.

[0255] A plurality of square fourth magnetic sheets 157 are formed by a specific number each beneath the first inner conductor 141 a and above the second inner conductor 142 i.

[0256] Magnetic sheets 150, 152, 154, 157 are composed of a mixture of oxide of ferrite powder and resin, and a flat square magnetic member 158 (not shown) is formed by laminating them in the vertical direction as described above. The magnetic member 158 may also have a certain thickness, not being limited to be flat. Or the magnetic member 158 is not always required to be square. The thickness may be adjusted properly depending on the required characteristics (impedance, withstand voltage, etc.), and the thickness may be adjusted by varying the thickness of the magnetic sheet itself, or by changing the number of magnetic sheets to be formed.

[0257] The magnetic member 158 is impregnated with fluorine silane coupling agent, and the water-repellent fluorine silane coupling agent permeates into fine pores in the magnetic member 158, so that the humidity resistance of the noise filter can be enhanced.

[0258] Of the external electrodes 159 a, 159 b, 159 c, 159 d (not shown) formed at both ends of the magnetic member 158, 159 a and 159 c are formed at one end of the magnetic member 158, and 159 b and 159 d are formed at other end of the magnetic member 158. The external electrodes 159 a, 159 b, 159 c, 159 d are plated with low melting metal such as nickel, tin or solder on the surface of silver or other conductors.

[0259] The external electrodes 159 a, 159 b, 159 c, 159 d may be also formed at four corners of the magnetic member 158 in a top view of the magnetic member 158.

[0260] Both ends of the first coil 141, that is, the first leading-out electrode 146 and second leading-out electrode 147 are electrically connected to the external electrode 159 a and external electrode 159 b, respectively.

[0261] Similarly, in the second coil 142, the third leading-out electrode 148 is electrically connected to the external electrode 159 c, and the fourth leading-out electrode 149 to the external electrode 159 d.

[0262] At this time, of the first inner conductor 141 e and second inner conductor 142 a, first inner conductor 141 f and second inner conductor 142 b, first inner conductor 141 g and second inner conductor 142 c, first inner conductor 141 h and second inner conductor 142 d, and first inner conductor 141 i and second inner conductor 142 e respectively formed on a same plane, the first inner conductors 141 c, 141 d, 141 e, 141 f, 141 g are formed inside of the second inner conductors 142 a, 142 b, 142 c, 142 d, 142 e.

[0263] As described herein, the noise filter in embodiment 4 of the invention comprises three layers, consisting of the first laminated body 143 composed of the first inner conductors 141 a to 141 d only, the second laminated body 144 formed on the first laminated body 143 composed of the first inner conductor 141 e and second inner conductor 142 a, first inner conductor 141 f and second inner conductor 142 b, first inner conductor 141 g and second inner conductor 142 c, first inner conductor 141 h and second inner conductor 142 d, and first inner conductor 141 i and second inner conductor 142 e respectively formed on a same plane, and the third laminated body 145 formed on the second laminated body 144 composed of the second inner conductors 142 f to 142 i only. Accordingly, when the current flows in a same direction in the first coil 141 and second coil 142 (clockwise or counterclockwise in a top view of the magnetic member 158), since the magnetic fluxes generated in the first inner conductors 141 a to 141 i and second inner conductors 142 a to 142 e of the second laminated body 144 reinforce each other, and the impedance in common mode is higher. Further, if current flows in reverse directions in the first coil 141 and second coil 142, since only the first inner conductors 141 a to 141 d are formed in the first laminated body 143 and only the second inner conductors 142 f to 142 i are formed in the third laminated body 145, the magnetic fluxes generated in the first inner conductors 141 a to 141 d formed in the first laminated body 143 and the second inner conductors 142 f to 142 i formed in the third laminated body 145 do not cancel each other, so that the impedance in normal mode may be enhanced.

[0264] Therefore, if a current flows in a same direction in the first coil 141 and second coil 142 (first inner conductors 141 e to 141 i and second inner conductors 142 a to 142 e in the second laminated body 144), the impedance in the first inner conductors 141 e to 141 i and second inner conductors 142 a to 142 e becomes high, and these inner conductors decrease the noise of the common mode. On the other hand, when flowing in opposite directions, the impedance becomes high in the first inner conductors 141 a to 141 d formed in the first laminated body 143 and the second inner conductors 142 f to 142 i formed in the third laminated body 145, and these inner conductors decrease the noise in normal mode.

[0265] The equivalent circuit diagram of the noise filter in embodiment 4 of the invention is also shown in FIG. 18.

[0266] Incidentally, when the number of inner conductors formed in the first laminated body 143 and the number of second inner conductors formed in third laminated body 145 are different, if a current flows in reverse directions in the first coil 141 and second coil 142, the intensity of magnetic fluxes generated in the first inner conductors formed in the first laminated body 143 and the second inner conductors formed in the third laminated body 145 is different, so that the impedance in normal mode entered from the first inner conductors may be set different from the impedance in normal mode entered from the second inner conductors.

[0267] As described above, in the second laminated body 144, since the first inner conductors 141 e, 141 f, 141 g, 141 h, 141 i are formed inside of the second inner conductors 142 a, 142 b, 142 c, 142 d, 142 e, the length between external electrodes (159 a and 159 b, 159 c and 159 d) in the first and second coils 141, 142 is different. As a result, the impedance values of the first and second coils 141, 142 differ, but such inconvenience may be eliminated by increasing the number of first inner conductors formed in the first laminated body 143 more than the number of second inner conductors formed in the third laminated body 145, and by equalizing the distance between external electrodes (159 a and 159 b, 159 c and 159 d) in the first and second coils 141, 142.

[0268] It is also effective to adjust the magnetic coupling coefficient finely.

[0269] That is, in this noise filter, the first and second coils 141, 142 are individually composed of nine layers, and five layers thereof, that is, about 56% are formed on the same plane, but by varying the rate of the portions formed on the same plane (the rate of the inner conductors formed in the second laminated body 144 of the whole inner conductors), the rate of inner conductors capable of mutually reinforcing the generated magnetic fluxes is changed, so that the coupling coefficient changes.

[0270] When the coupling coefficient can be thus finely adjusted, the impedance in common mode and impedance in normal mode can be controlled to specified values, and this effect is outstanding.

[0271] Further, by maximizing or minimizing the rate of portions formed on the same plane, the coupling coefficient can be adjusted to a specified value between 0.2 to 0.95, and the impedance in normal mode and common mode can be adjusted.

[0272] Further, if the specified impedance in normal mode is obtained, the shape of the first inner conductors 141 a to 141 d formed in the first laminated body 143, and the shape of the second inner conductors 142 f to 142 i formed in the third laminated body 145 may not be limited, including the spiral, meandering or other shape formed on one plane. There is no problem if winding direction is reverse.

[0273] Incidentally, by bringing the first inner conductors 141 e to 141 i and second inner conductors 142 a to 142 e in the second laminated body 144 as close to one turn as possible, the length of each inner conductor may be extended to a maximum extent, and therefore the magnetic fluxes generated in the first inner conductors 141 e to 141 i, and the second inner conductors 142 a to 142 e can reinforce each other, and if a current flows in a same direction in the first coil 141 and second coil 142 (the first inner conductors 141 e to 141 i and the second inner conductors 142 a to 142 e in the second laminated body 144), the impedance in common mode can be further enhanced.

[0274] The manufacturing method is same as in embodiment 3 of the invention, basically, except that the forming positions of the inner conductors are different, and the explanation is omitted.

[0275] Herein, by setting the interval of the adjacent first inner conductors 141 a to 141 d and second inner conductors 142 f to 142 i in the first laminated body 143 and third laminated body 145 larger than the interval of the first inner conductors and second inner conductors formed on a same plane in the second laminated body 144 (between the first inner conductor 141 e and second inner conductor 142 a, 141 f and 142 b, 141 g and 142 c, 141 h and 142 d, and 141 i and 142 e), it is effective to decrease the floating capacity generated in the adjacent first inner conductors 141 a to 141 d and second inner conductors 142 f to 142 i in the first laminated body 143 and third laminated body 145, and in the first inner conductors 141 a to 141 d in the first laminated body 143 and the second inner conductors 142 f to 142 i in the third laminated body 145. Accordingly, the impedance is enhanced in the high frequency region, and the distance between the first inner conductors 141 a to 141 d in the first laminated body 143 and the second inner conductors 142 f to 142 i in the third laminated body 145 can be extended, and therefore, the magnetic fluxes generated in the first inner conductors 141 a to 141 d in the first laminated body 143 and the second inner conductors 142 f to 142 i in the third laminated body 145 do not cancel each other, and the impedance in normal mode is enhanced.

[0276] Further, by forming a sheet of a lower permeability than that of the magnetic member 138 between the adjacent first inner conductors 141 a to 141 d and second inner conductors 142 f to 142 i in the first laminated body 143 and third laminated body 145, the magnetic fluxes generated in the first inner conductors 141 a to 141 d in the first laminated body 143 and the second inner conductors 142 f to 142 i in the third laminated body 145 can be weakened, so that the impedance in normal mode can be lowered. Therefore, when the impedance in common mode is constant, by controlling the impedance in normal mode, the coupling coefficient can be adjusted.

[0277] Also by equalizing the length among the external electrodes in the first and second coils 141, 142 (between 159 a and 159 b, and 159 c and 159 d), the total coil length including the leading-out portions is equal, so that the impedance values may be same in the first and second coils 141, 142.

[0278] Moreover, by setting the density of the magnetic member in the adjacent first coil 141 and second coil 142 in the second laminated body 144 (the first inner conductor 141 e and second inner conductor 142 a, 141 f and 142 b, 141 g and 142 c, 141 h and 142 d, and 141 i and 142 e) higher than that of the magnetic member in other parts (first laminated body 143, third laminated body 145), it is effective to lower the porosity between the first coil 141 and second coil 142 in the laminated body 144, so that the withstand-voltage between the first coil 141 and second coil 142 in the second laminated body 144 may be maintained.

[0279] In the foregoing embodiments 3 and 4 of the invention, by setting the distance between the first laminated body 123, 143 and the second laminated body 124, 144 (between the first inner conductor 121 c and second inner conductor 122 a, between the first inner conductor 141 d and second inner conductor 142 a), and between the second laminated body 124, 144 and the third laminated body 125, 145 (between the first inner conductor 121 f and second inner conductor 122 d, between the first inner conductor 141 i and second inner conductor 142 f) longer than the distance between the adjacent inner conductors in the first laminated body 123, 143, second laminated body 124, 144, and third laminated body 125, 145, it is effective to decrease the floating capacity generated in the first inner conductors 121 a to 121 c, 141 a to 141 d in the first laminated body 123, 143, and second inner conductors 122 d to 122 f, 142 f to 142 i in the third laminated body 125, 145 Accordingly, the impedance is enhanced in the high frequency region, and the distance between the first inner conductors 121 a to 121 c, 141 a to 141 d in the first laminated body 123, 143 and the second inner conductors 122 d to 122 f, 142 f to 142 i in the third laminated body 125, 145 can be extended, and therefore, the magnetic fluxes generated in the first inner conductors 121 a to 121 c, 141 a to 141 d in the first laminated body 123, 143 and the second inner conductors 122 d to 122 f, 142 f to 142 i in the third laminated body 125, 145 do not cancel each other, and the impedance in normal mode is enhanced.

[0280] Further, by forming magnetic sheets of a lower permeability than that of the other magnetic sheets between the first laminated body 123, 143 and second laminated body 124, 144, and between the second laminated body 124, 144 and third laminated body 125, 145, the magnetic fluxes generated in the first inner conductors 121 a to 121 c, 141 a to 141 d in the first laminated body 123, 143 and the second inner conductors 122 d to 122 f, 142 f to 142 i in the third laminated body 125, 145 do not cancel each other, so that the impedance in normal mode may be enhanced.

[0281] (Embodiment 5)

[0282]FIG. 22 is a perspective exploded view of a noise filter in embodiment 5 of the invention, FIG. 23(a) is a sectional view of line A-A in FIG. 22, and FIG. 23(b) is a top see-through diagram of the noise filter.

[0283] A spiral first coil 161 is formed by laminating and connecting first inner conductors 161 a to 161 d sequentially from the bottom. A spiral second coil 162 is formed by laminating and connecting second inner conductors 162 a to 162 d sequentially from the bottom. That is, the first and second coils 161, 162 are composed of four layers. The first and second coils 161, 162 are not required to have four-layer structure. The first inner conductors 161 a to 161 d and second inner conductors 162 a to 162 d are made of silver or other conductive material.

[0284] The first inner conductors 161 a to 161 d and second inner conductors 162 a to 162 d are formed in U-shape except for the lowest and highest layers thereof 161 a, 161 d, 162 a, 162 d. Not limited to U-shape, they may be formed in L- or other shape.

[0285] The first inner conductor 161 a, second inner conductor 162 a, first inner conductor 161 b, second inner conductor 162 b, first inner conductor 161 c, second inner conductor 162 c, and first inner conductor 161 d, second inner conductor 162 d are sequentially laminated from the bottom, that is, the first inner conductors 161 a to 161 d and second inner conductors 162 a to 162 d are formed alternately. Further, as shown in FIG. 23(b), in a top view of the second inner conductor 162 d (a top view of a magnetic member 171 mentioned below), the area enclosed by the first coil 161 and the area enclosed by the second coil 162 are formed to overlap only in part individually.

[0286] That is, supposing the central axis of the spiral first coil 162 to be B and the central axis of the spiral second coil 161 to be C, B and C are deviated.

[0287] Herein, B and C are deviated to such an extent that the area enclosed by the first coil 161 and the area enclosed by the second coil 162 may overlap completely, or may not overlap completely in a top view (a top view of the magnetic member 171 mentioned below) of the second inner conductor 162 d of the first and second coils 161, 162.

[0288] In the lowest layer and highest layer 161 a, 161 d of the first inner conductors 161 a to 161 d, first and second leading-out electrodes 163, 164 are formed as the ends of the first coil 161. Similarly, third and fourth leading-out electrodes 165, 166 are formed in the second inner conductors 162 a, 162 d.

[0289] The leading-out electrodes 163, 164, 165, 166 may be also formed at four corners of the magnetic member 171 in a top view of the second inner conductor 162 d (magnetic member 171 described below).

[0290] A plurality of square first magnetic sheets 167 are formed beneath the first inner conductors 161 b to 161 d, and second inner conductors 162 a to 162 d, and a first via hole 168 and a second via hole 169 are formed (only the first via hole 168 is formed in the first magnetic sheet 167 formed beneath the second inner conductor 162 a, and only the second via hole 169 is formed in the first magnetic sheet 167 formed beneath the second inner conductor 162 d).

[0291] Through the first via hole 168, the first inner conductors 161 a and 161 b, 161 b and 161 c, and 161 c and 161 d are connected. Through the second via hole 169, similarly, the second inner conductors 162 a and 162 b, 162 b and 162 c, and 162 c and 162 d are connected.

[0292] That is, the second via hole 169 is formed in the first magnetic sheet 167 having the first via hole 168 beneath the first inner conductor 161 b. The first inner conductor 161 b is connected to the first via hole 168 and the first inner conductor 161 a through the first via hole 168 disposed in the first magnetic sheet 167 formed beneath it (above the first inner conductor 161 a), and the second inner conductor 162 b is connected to the second via hole 169 and the second inner conductor 162 a through the second via hole 169 disposed in the first magnetic sheet 167 formed above it (beneath the inner conductor 162 b).

[0293] The first via hole 168 and second inner conductors 162 a to 162 d,and the second via hole 169 and first inner conductors 161 a to 161 d are electrically insulated from each other.

[0294] A plurality of square second magnetic sheets 170 are formed by a specified number of sheets beneath the first inner conductor 161 a and above the second inner conductor 162 d.

[0295] Magnetic sheets 167, 170 are composed of a mixture of oxide of ferrite powder and resin, and a flat square magnetic member 171 is formed by laminating them in the vertical direction as described above. The magnetic member 171 may also have a certain thickness, not being limited to be flat. Or the magnetic member 171 is not always required to be square. The thickness may be adjusted properly depending on the required characteristics (impedance, withstand voltage, etc.), and the thickness may be adjusted by varying the thickness of the magnetic sheet itself, or by changing the number of magnetic sheets to be formed.

[0296] The magnetic member 171 is impregnated with fluorine silane coupling agent, and the water-repellent fluorine silane coupling agent permeates into fine pores in the magnetic member 171, so that the humidity resistance of the noise filter can be enhanced.

[0297] Of the external electrodes 172 a, 172 b, 172 c, 172 d (not shown) formed at both ends of the magnetic member 171, 172 a and 172 c are formed at one end of the magnetic member 171, and 172 b and 172 d are formed at other end of the magnetic member 171. The external electrodes 172 a, 172 b, 172 c, 172 d are plated with low melting metal such as nickel, tin or solder on the surface of silver or other conductors.

[0298] The external electrodes 172 a, 172 b, 172 c, 172 d may be also formed at four corners of the magnetic member 171 in a top view of the magnetic member 171.

[0299] Both ends of the first coil 161, that is, the first leading-out electrode 163 and second leading-out electrode 164 are electrically connected to the external electrode 172 a and external electrode 172 b, respectively.

[0300] Similarly, in the second coil 162, the third leading-out electrode 165 is electrically connected to the external electrode 172 c, and the fourth leading-out electrode 166 to the external electrode 172 d.

[0301] As shown in FIG. 24, meanwhile, the central axis B of the spiral first coil 161 and the central axis C of the spiral second coil 162 may be deviated as explained in embodiment 5 of the invention, and it may be designed to comprise, as in embodiment 3 of the invention, a first laminated body composed of the first inner conductors only, a second laminated body formed on the top of the first laminated body, alternately laminating the first inner conductors and second inner conductors, and a third laminated body formed on the top of the second laminated body, composed of the second inner conductors only.

[0302] Or, as shown in FIG. 25(a), in a top view of the magnetic member 171, the area enclosed by the first coil 161 and the area enclosed by the second coil 162 may cross orthogonally in the portion shown in FIG. 23(b), or as shown in FIG. 5(b), in a top view of the magnetic member 171, the overlapping portion of the area enclosed by the first coil 161 and the area enclosed by the second coil 162 may be diagonal.

[0303] Further, as shown in FIGS. 26(a), (b), spiral first and second coils 161′, 162′ may overlap in part in a top view of the magnetic member.

[0304] As described herein, in the noise filter in embodiment 5 of the invention, the spiral first coil 161 composed of first inner conductors 161 a to 161 d and spiral second coil 162 composed of second inner conductors 162 a to 162 d are formed to overlap only in part, in the area enclosed by the first coil 161 and the area enclosed by the second coil 162, in a top view of the magnetic member 171. When a current flows in a same direction in the first coil 161 and second coil 162 (clockwise or counterclockwise in a top view of the magnetic member 171), since the first inner conductors 161 a to 161 d and second inner conductors 162 a to 162 d are formed alternately, the distance of the alternately formed mutually adjacent first inner conductors 161 a to 161 d and second inner conductors 162 a to 162 d is closer. As a result, in a top view of the magnetic member 171 in the first coil 161 and second coil 162, the magnetic fluxes generated in the overlapped portions of area enclosed by the first coil 161 and the area enclosed by the second coil 162 can reinforced with each other, and the impedance in common mode is enhanced, and if a current flows in opposite directions in the first coil 161 and second coil 162, in a top view of the magnetic member 171 in the first coil 161 and second coil 162, the magnetic fluxes generated in the non-overlapped portions of area enclosed by the first coil 161 and the area enclosed by the second coil 162 do not cancel each other, so that the impedance in normal mode may be enhanced.

[0305] Therefore, when a current flows in a same direction in the first coil 161 (first inner conductors 161 a to 161 d) and second coil 162 (second inner conductors 162 a to 162 d), the impedance becomes higher in the overlapped portion in a top view of the magnetic member 171 in the first coil 161 and second coil 162, and this portion lowers the noise in common mode. If flowing in opposite directions, to the contrary, the impedance becomes high in the non-overlapped portion in a top view of the magnetic member 171 in the first coil 161 and second coil 162, and this portion lowers the noise in normal mode.

[0306]FIG. 27 is an equivalent circuit diagram of the noise filter in embodiment 5 of the invention. In the first coil 161 and second coil 162 for heightening the impedance in normal mode, when the area is equal in the non-overlapped portion in a top view of the magnetic member 171 in the enclosed portion of the first coil 161 and enclosed portion of the second coil 162, the impedance in normal mode is equal, so that there is no directivity.

[0307] If the area is not equal in the non-overlapped portion in a top view of the magnetic member 171 in the enclosed portion of the first coil 161 and enclosed portion of the second coil 162, when a current flows in opposite directions in the first coil 161 and second coil 162, the intensity of magnetic fluxes generated in the first coil 161 and second coil 162 is different. As a result, the impedance in normal mode entered from the first coil 161 is different from the impedance in normal mode entered from the second coil 162.

[0308] Further, the magnetic coupling coefficient can be adjusted finely. That is, in this noise filter, by varying the overlapped portion area of the first and second coils 161, 162 in a top view of the magnetic member 171, the rate of the inner conductors for reinforcing the generated magnetic fluxes mutually varies, so that the coupling coefficient is changed.

[0309] When the coupling coefficient can be thus finely adjusted, the impedance in common mode and impedance in normal mode can be individually set to desired values, and this effect is outstanding.

[0310] Further, by maximizing or minimizing the area of overlapped portions of the first and second coils 161, 162 in a top view of the magnetic member 171, the coupling coefficient can be adjusted to a specified value between 0.2 to 0.95, and the impedance in normal mode and common mode can be adjusted.

[0311] Further, if the specified impedance in normal mode is obtained, the shape of the first inner conductors 161 a to 161 d and second inner conductors 162 a to 162 d may not be limited, including the spiral, meandering or other shape. There is no problem if winding direction is reverse.

[0312] Incidentally, by bringing the first inner conductors 161 a to 161 d and second inner conductors 162 a to 162 d as close to one turn as possible, the length of each inner conductor may be extended to a maximum extent, and therefore the magnetic fluxes generated in the first inner conductors 161 a to 161 d and second inner conductors 162 a to 162 d can reinforce each other, and if a current flows in a same direction in the first coil 161 and second coil 162, the impedance in common mode can be further enhanced.

[0313] The manufacturing method is same as in embodiment 3 of the invention, basically, except that the forming positions of the inner conductors are different, and the explanation is omitted.

[0314] Herein, by equalizing the length among the external electrodes in the first and second coils 161, 162 (between 172 a and 172 b, and 172 c and 172 d), the total coil length including the leading-out portions is equal, so that the impedance values may be same in the first and second coils 161, 162.

[0315] Moreover, by setting the density of the magnetic member in the adjacent first inner conductors of the first coil 161 and second inner conductors of the second coil 162 (the inner conductor 161 a and second inner conductor 162 a, 162 a and 161 b, 161 b and 162 b, etc.) higher than that of the magnetic member in other inner conductors, it is effective to lower the porosity between the first coil 161 and second coil 162 (between the adjacent first inner conductor and second inner conductor each), so that the withstand voltage may be maintained between the first inner conductor 161 a and second inner conductor 162 a, 162 a and 161 b, 161 b and 162 b (between the first coil 161 and second coil 162).

[0316] In the noise filters in the foregoing embodiments 3 to 5 of the invention, the junctions of a pair of external electrodes formed at one end of the magnetic member and the first coil and second coil electrically connected to the external electrodes are formed above or beneath, in a side view of the magnetic member, the junctions of a pair of external electrodes formed at other end of the magnetic member and the first coil and second coil electrically connected to the external electrodes, and therefore if the direction is different when mounting on the board, the attenuation characteristics are not changed.

[0317] In the noise filters in the foregoing embodiments 3 to 5 of the invention, further as shown in FIG. 28(a) (which shows a sectional view of the noise filter in embodiment 5 of the invention as an example), the junctions 181 a, 181 b of a pair of external electrodes 181 formed at one end of the magnetic member 171 and the first coil 161 and second coil 162 electrically connected thereto are formed above, in a side view of the magnetic member 171, the junctions 182 a, 182 b of a pair of external electrodes 182 formed at other end of the magnetic member 171 and the first coil 161 and second coil 162 electrically connected thereto (pattern A). The equivalent circuit diagram of pattern A is shown in FIG. 18.

[0318] At this time, in a side view of the magnetic member 171, the junction 181 a of the external electrode 181 formed at one end of the magnetic member 171 and the first coil 161, the junction 181 b of the external electrode 181 formed at one end of the magnetic member 171 and the second coil 162, the junction 182 a of the external electrode 182 formed at other end of the magnetic member 171 and the first coil 161, and the junction 182 b of the external electrode 182 formed at other end of the magnetic member 171 and the second coil 162 are formed sequentially from the top. It is same if the first coil 161 and second coil 162 are exchanged.

[0319] By contrast, the junctions 181 a, 181 b of a pair of external electrodes 181 formed at one end of the magnetic member 171 and the first coil 161 and second coil 162 electrically connected thereto may be formed, as shown in FIG. 28(b), either above or beneath, in a side view of the magnetic member 171, the junctions 182 a, 182 b of a pair of external electrodes 182 formed at other end of the magnetic member 171 and the first coil 161 and second coil 162 electrically connected thereto, or, as shown in FIG. 28(c), may be formed between the junctions 182 a and 182 b (pattern B). FIG. 28(c) shows the mounting direction is changed (inverted) from the configuration in FIG. 28(b).

[0320]FIG. 28(d) shows the relation (attenuation characteristics) of frequency and attenuation of noise filters of pattern A and pattern B in embodiments 3 to 5 of the invention. The same samples as in FIG. 19 were used. In the diagram, A, B, C correspond to FIGS. 28(a), (b), (c).

[0321] As clear from FIG. 28(d), in embodiments 3 to 5 of the invention, the noise filter of pattern A is free from fluctuation in the attenuation characteristics, but pattern B fluctuates (when the current direction is changed). The equivalent circuit diagram of pattern B is shown in FIG. 29.

[0322] This is because, in the noise filters of pattern A in embodiments 3 to 5 of the invention, the distance between the junctions 181 a and 181 b of a pair of external electrodes 181 formed at one end of the magnetic member 171 and the first coil 161 and second coil 162, and the distance between the junctions 182 a and 182 b of a pair of external electrodes 182 formed at other end of the magnetic member 171 and the first coil 161 and second coil 162 are equal to each other, and therefore if the applied direction of the normal mode current is different (the current entering from 181 a and leaving from 182 a further enters from 182 b and leaves from 181 a, or the current entering from 182 a and leaving from 181 a further enters from 181 b and leaves from 182 a), the floating capacity generated in the magnetic member 171 (the floating capacity between the vicinity of input and vicinity of output) is not changed. As a result, if the direction of mounting on the board is different, the attenuation characteristics are invariable.

[0323] In embodiments 3 and 4, if the number of inner conductors for composing the first and second coils is equal, the impedance values in normal mode are equal, so that directivity does not exist.

[0324] When the noise filter in embodiments 3 to 5 of the invention is applied in a pair of signal lines in cellular phone or other wireless communication appliance, the same effects as in embodiment 1 and 2 shown in FIGS. 15(a), (b), (c) are obtained.

[0325] (Embodiment 6)

[0326] A common mode noise filter in embodiment 6 of the invention is explained by referring to the drawings.

[0327]FIG. 30 is a perspective exploded view of the common mode noise filter in embodiment 6 of the invention, FIG. 31(a) is a sectional view of line A-A of the same, and FIG. 31(b) is a perspective view thereof.

[0328] In FIG. 30 and FIG. 31, a spiral first coil 231 is formed by laminating and connecting first inner conductors 231 a to 231 e sequentially from the bottom. A spiral second coil 232 is formed by laminating and connecting second inner conductors 232 a to 232 e sequentially from the bottom. That is, the first and second coils 231, 232 are composed of five layers. However, the first and second coils 231, 232 are not limited to five-layer structure. The first inner conductors 231 a to 231 e and second inner conductor 232 a to 232 e are made of silver or other conductive material.

[0329] Herein, the first inner conductors 231 a to 231 e and second inner conductors 232 a to 232 e are formed alternately.

[0330] That is, the first inner conductor 231 a, second inner conductor 232 a, first inner conductor 231 b, second inner conductor 232 b, first inner conductor 231 c, second inner conductor 232 c, first inner conductor 231 d, second inner conductor 232 d, first inner conductor 231 e, and second inner conductor 232 e are sequentially formed from the bottom.

[0331] The spiral first coil 231 formed by laminating the first inner conductors 231 a to 231 e and the spiral second coil 232 formed by laminating the second inner conductors 232 a to 232 e are formed to overlap with each other in a top view of a magnetic member 246 described below.

[0332] The first inner conductors 231 a to 231 e and second inner conductors 232 a to 232 e are formed in a nearly U-shape.

[0333] By forming in a nearly U-shape, a coil of one turn is formed by laminating the inner conductors by two layers only, and the number of layers may be smaller. As a result, the size is reduced, and the distance of adjacent inner conductors is closer in each inner conductor for forming the coil, so that the magnetic fluxes generated in the first and second coils 231, 232 can reinforce each other.

[0334] Beneath the lowest layer 231 a of the first inner conductors 231 a to 231 e, a first leading-out electrode 233 for connecting with the end of the first coil 231 is formed, and above the highest layer 231 e, a second leading-out electrode 234 for connecting with the other end of the first coil 231 is formed. Similarly, in the second inner conductors 232 a, 232 e, third and fourth leading-out electrodes 235, 236 are formed.

[0335] The leading-out electrodes 233, 234, 235, 236 may be also formed at four corners of the magnetic member 246 in a top view of the magnetic member 246.

[0336] A plurality of square first magnetic sheets 237 are formed beneath the first inner conductors 231 b to 231 e, and are provided with a first via hole 238 and a second via hole 239. The first via hole 238 is connected to each end of the first inner conductors 231 a to 231 e, and is electrically insulated from the second via hole 239.

[0337] The second via hole 239 is formed to overlap with the first and second coils 231, 231 in a top view of the magnetic member 246.

[0338] A plurality of square second magnetic sheets 240 are formed beneath the second inner conductors 232 a to 232 e, and are provided with a third via hole 241 and a fourth via hole 242. The fourth via hole 242 is connected to each end of the second inner conductors 232 a to 232 e, and is electrically insulated from the third via hole 241.

[0339] The third via hole 241 is formed to overlap with the first and second coils 231, 232 in a top view of the magnetic member 246.

[0340] At this time, the first inner conductors 231 a to 231 e are connected through the first via hole 238 and third via hole 241, and the spiral first coil 231 is obtained. Similarly, the second inner conductors 232 a to 232 e are connected through the second via hole 239 and fourth via hole 242, and the spiral second coil 232 is obtained.

[0341] That is, the second via hole 239 is formed in the first magnetic sheet 237 having the first via hole 238 beneath the first inner conductor 231 b. The first inner conductor 231 b is connected to the first inner conductor 231 a through the first via hole 238 and third via hole 241 provided in the second magnetic sheet 240 further beneath it (above the first inner conductor 231 a), and the second inner conductor 232 b is connected to the second inner conductor 232 a through the second via hole 239 and fourth via hole 242 provided in the second magnetic sheet 240 further above it (beneath the second inner conductor 232 b).

[0342] The first inner conductors 231 a to 231 e and at least one of the second inner conductors 232 a to 232 e adjacent to the first inner conductors 231 a to 231 e are formed to nearly overlap in a top view of the magnetic member 246.

[0343] That is, each pair of first inner conductor 231 a and second inner conductor 232 a, first inner conductor 231 b and second inner conductor 232 b, first inner conductor 231 c and second inner conductor 232 c, first inner conductor 23 id and second inner conductor 232 d, and first inner conductor 231 e and second inner conductor 232 e are provided to overlap in a top view of the magnetic member 246 (except for the formed portions of the via holes 238, 239, 241, 242).

[0344] A plurality of square third magnetic sheets 243 are formed beneath the first inner conductor 231 a and above the second inner conductors 232 e. Beneath the third magnetic sheet 243 formed beneath the first inner conductor 231 a, first and third leading-out electrodes 233, 235 are provided, and above the third magnetic sheet 243 formed above the second inner conductor 231 e, second and fourth leading-out electrodes 234, 236 are provided.

[0345] A fifth via hole 244 is provided in the third magnetic sheet 243 formed on the top of the second inner conductor 232 e, and the second inner conductor 232 e and fourth leading-out electrode 236, and the first inner conductor 231 e and (through the third via hole 241) second leading-out electrode 234 are connected with each other respectively through the fifth via hole 244.

[0346] Further, first and second via holes 238, 239 are provided in the third magnetic sheet 243 formed beneath the first inner conductor 231 a, and the first inner conductor 231 a and first leading-out electrode 233, and the second inner conductor 232 a and (through the second via hole 239) third leading-out electrode 235 are connected with each other respectively through the first and second via holes 238, 239.

[0347] A specified number of fourth magnetic sheets 245 are formed beneath the first and third leading-out electrodes 233, 235, and above the second and fourth leading-out electrodes 234, 236.

[0348] Magnetic sheets 237, 240, 243, 245 are composed of a mixture of oxide of ferrite powder and resin, and a flat square magnetic member 246 is formed by laminating them in the vertical direction as described above. The magnetic member 246 may also have a certain thickness, not being limited to be flat. Or the magnetic member 246 is not always required to be square. The thickness may be adjusted properly depending on the required characteristics (impedance, withstand voltage, etc.), and the thickness may be adjusted by varying the thickness of the magnetic sheet itself, or by changing the number of magnetic sheets to be formed.

[0349] The magnetic member 246 is impregnated with fluorine silane coupling agent, and the water-repellent fluorine silane coupling agent permeates into fine pores in the magnetic member 246, so that the humidity resistance of the noise filter can be enhanced.

[0350] Of the external electrodes 247 a, 247 b, 247 c, 247 d formed at both ends of the magnetic member 246, 247 a and 247 c are formed at one end of the magnetic member 246, and 247 b and 247 d are formed at other end of the magnetic member 246. The external electrodes 247 a, 247 b, 247 c, 247 d are plated with low melting metal such as nickel, tin or solder on the surface of the conductors of silver or the like.

[0351] The external electrodes 247 a, 247 b, 247 c, 247 d may be also formed at four corners of the magnetic member 246 in a top view of the magnetic member 246.

[0352] The first leading-out electrode 233 and second leading-out electrode 234 connected to both ends of the first coil 231 are electrically connected to the external electrode 247 a and external electrode 247 b, respectively.

[0353] Similarly, in the second coil 232, the third leading-out electrode 235 is electrically connected to the external electrode 247 c, and the fourth leading-out electrode 236 to the external electrode 247 d.

[0354] In the common mode noise filter in embodiment 6 of the invention having such configuration, the manufacturing method is explained below by referring to the drawings.

[0355] FIGS. 32(a) to (c), and FIGS. 33(a) to (d) are perspective views showing the manufacturing method of the common mode noise filter in embodiment 6 of the invention.

[0356] First, from a mixture of oxide of ferrite powder and resin, square first magnetic sheet 237, second magnetic sheet 240, third magnetic sheet 243, and fourth magnetic sheet 245 are fabricated.

[0357] Next, as shown in FIG. 32(a), a fifth via hole 244 is opened in a specified position of the third magnetic sheet 243 by laser, punching or other drilling process.

[0358] Similarly, first and second via holes 238, 239 are provided at specified positions of the first magnetic sheet 237. Third and fourth via holes 241, 242 are provided at specified positions of the second magnetic sheet 240, and first and second via holes 238, 239 are provided at specified positions of the third magnetic sheet 243.

[0359] As shown in FIG. 32(b), second leading-out electrode 234 and fourth leading-out electrode 236 are formed on the third magnetic sheet 243 having the fifth via hole 244. At the same time, the fifth via hole 244 is filled with silver or other conductive material.

[0360] The first inner conductor 231 a is printed on the third magnetic sheet 243 having the first via hole 238 and second via hole 239. The first via hole 238 and first leading-out electrode 233 are connected to the second via hole 239 and third leading-out electrode 235. At the same time, the first via hole 238 and second via hole 239 are filled with silver or other conductive material.

[0361] The second inner conductor 232 a is printed on the second magnetic sheet 240. The end of the second inner conductor 232 a and the fourth via hole 242 are connected. At the same time, the third via hole 241 and fourth via hole 242 are filled with silver or other conductive material.

[0362] The first inner conductor 231 b is printed on the first magnetic sheet 237. The end of the first inner conductor 231 b and the first via hole 238 are connected. At the same time, the first via hole 238 and second via hole 239 are filled with silver or other conductive material.

[0363] The first and third leading-out electrodes 233, 235 are printed on the fourth magnetic sheet 245.

[0364] Same as above, the plurality of first magnetic sheets 237 and second magnetic sheets 240 are alternately laminated, and set in configuration as shown in FIG. 32(c). A specified number of fourth magnetic sheets 245 are formed beneath the first and third leading-out electrodes 233, 235, and above the second and fourth leading-out electrodes 234, 236.

[0365] At this time, by the first via hole 238 formed in the first magnetic sheet 237 and the third via hole 241 formed in the second magnetic sheet 240, the first inner conductors 231 a to 231 e are connected, and the first coil 231 is obtained. By the second via hole 239 formed in the first magnetic sheet 237 and the fourth via hole 242 formed in the second magnetic sheet 240, the second inner conductors 232 a to 232 e are connected, and the second coil 232 is obtained.

[0366] Through the fifth via hole 244 formed in the third magnetic sheet 243, the second inner conductor 232 e and fourth leading-out electrode 236, and the first inner conductor 231 e and (through the third via hole 241) second leading-out electrode 234 are connected respectively.

[0367] Further, through the first via hole 238 formed in the third magnetic sheet 243, the first inner conductor 231 a and first leading-out electrode 233 are connected with each other, and the through the fourth via hole 242 formed beneath the second magnetic sheet 240, the second inner conductor 232 a and (through the second via hole 239) third leading-out electrode 235 are connected with each other.

[0368] The inner conductors and leading-out electrodes may be formed not only by printing, but also by plating, vapor deposition, sputtering or other method.

[0369] Next, as shown in FIG. 33(a), by cutting off so that the first coil 231 and second coil 232 may be incorporated by one piece each in one common mode noise filter, one laminated body 248 is obtained as shown in FIG. 33(b). At this time, the first leading-out electrode 233 and third leading-out electrode 235 are exposed from both ends of the laminated body 248, and the second leading-out electrode 234 and fourth leading-out electrode 236 are exposed at other ends.

[0370] This laminated body 248 is baked, and a magnetic member 246 is formed.

[0371] The magnetic member 246 is chamfered as shown in FIG. 33(c).

[0372] Finally, as shown in FIG. 33(d), silver or other conductors are formed in the leading-out electrodes 233, 234, 235, 236 exposed at both ends of the magnetic member 246, and their surfaces are plated with low melting metal such as nickel, tin or solder, and the external electrode 247 a is formed in the first leading-out electrode 233, external electrode 247 b is formed in the second leading-out electrode 234, external electrode 247 c is formed in the third leading-out electrode 235, and external electrode 247 d is formed in the fourth leading-out electrode 236, so that the common mode noise filter in embodiment 6 of the invention is manufactured.

[0373] After forming silver or other conductors, and before nickel plating, the magnetic member 246 is impregnated in fluorine silane coupling agent in decompressed atmosphere.

[0374] In the common mode noise filter in embodiment 6 of the invention, since the first coil 231 and second coil 232 overlap in a top view of the magnetic member 246, and the first inner conductors 231 a to 231 e and at least one of the second inner conductors 232 a to 232 e adjacent to these first inner conductors 231 a to 231 e are designed to overlap nearly in a top view of the magnetic member 246, if a current flows in a same direction in the first coil 231 and second coil 232 (clockwise or counterclockwise in a top view of the magnetic member), the magnetic fluxes generated in the first inner conductors 231 a to 231 e and second inner conductors 232 a to 232 e reinforce each other, and further the magnetic fluxes generated in the adjacent first inner conductors 231 a to 231 e and second inner conductors 232 a to 232 e reinforce each other, in particular. As a result, the impedance in common mode can be further enhanced.

[0375] Therefore, when a current flows in a same direction in the first coil 231 and second coil 232, the impedance in first inner conductors 231 a to 231 e and second inner conductors 232 a to 232 e becomes higher, and these inner conductors decrease the noise in common mode.

[0376] Further, since the second via hole 239 and third via hole 241 are formed to overlap with the first and second coils 231, 232 in a top view of the magnetic member 246, the second via hole 239 and (vertically) connected second inner conductors 232 a to 232 e can overlap with the first coil 231 composed of the first inner conductors 231 a to 231 e in a top view of the magnetic member 246. Similarly, the third via hole 241 and (vertically) connected first inner conductors 231 a to 231 e can overlap with the second coil 232 composed of the second inner conductors 232 a to 232 e in a top view of the magnetic member 246. Thus, the first and second coils 231, 232 always overlap in a top view of the magnetic member 246, so that the impedance in common mode may be effectively enhanced. On the other hand, if the second via hole 239 and third via hole 241 do not overlap with the first and second coils 231, 232 in a top view of the magnetic member 246, the second via hole 239 and (vertically) connected second inner conductors 232 a to 232 e, and the third via hole 241 and (vertically) connected first inner conductors 231 a to 231 e do not overlap with the first and second coils 231, 232 in a top view of the magnetic member 246, near the connection area of the second via hole 239 and third via hole 241 in the inner conductors 231 a to 231 e, 232 a to 232 e.

[0377] Of course, since the first via hole 238 and fourth via hole 242 are connected to the ends of the inner conductors 231 a to 231 e, 232 a to 232 e, they overlap with the first and second coils 231, 232 in a top view of the magnetic member 246.

[0378] By equalizing the length of the first and second coils 231, 232 including the leading-out electrodes 233 to 236, the impedance values in the first and second coils 231, 232 may be equalized.

[0379] A method of using the common mode noise filter in embodiment 6 of the invention in a pair of signal lines in a cellular phone or other wireless communication device as an example of electronic appliance is explained below.

[0380] Signal lines of communication wires such as a headset of a cellular phone, for example, are usually composed of a pair of cables (signal lines), and since the high frequency signal such as carrier of cellular phone is superposed on the cable as radiation noise in normal mode and common mode, the effect of noise is likely to appear. For example, the radiation noise superposed in common mode may appear as noise of audio signal.

[0381] Audio and other signals are disturbed by high frequency noise of common mode because the low frequency components in the signal are detected and superposed by the nonlinear element and electrostatic capacity in the circuit.

[0382] For example, as shown in FIG. 34(a), when the carrier 900 MHz (TDMA carrier) in the transmission and reception circuit of a cellular phone of TDMA system is transmitted and received at 217 Hz (burst frequency), 217 Hz is detected, and is superposed on the audio signal in normal mode, and audible noise is heard. Therefore, if the induced current in common mode can be suppressed, noise of audio output or the like can be lowered.

[0383] An example of use of the common mode noise filter in embodiment 6 of the invention is shown in FIG. 34(b).

[0384]FIG. 34(c) is a diagram showing the attenuation characteristic (relation between frequency and attenuation) of the common mode noise filter in embodiment 6 of the invention.

[0385] As clear from FIG. 34(c), even at the carrier 900 MHz of the cellular phone, the common mode noise is attenuated. Therefore, the signal of repetitive frequency 217 Hz detected together with the carrier 900 MHz can be lowered, so that the audible noise may not be heard.

INDUSTRIAL APPLICABILITY

[0386] As described herein, according to the invention, a noise filter high in impedance in common mode and normal mode, and a common mode noise filter high in impedance in common mode can be realized. When they are applied in signal lines in cellular phone or other wireless communication devices, noise can be attenuated. For example, in audio lines as a pair of signal lines, the audible noise can be reduced. 

1. A noise filter comprising a magnetic member formed by laminating magnetic sheets, a first impedance element formed in said magnetic member, a second impedance element formed above said first impedance element, and external electrodes formed at both ends of said magnetic member and connected electrically to each end of said first and second impedance elements, wherein said first impedance element includes a first normal impedance element and a first common impedance element connected electrically to said first normal impedance element above said first normal impedance element, said second impedance element includes a second common impedance element and a second normal impedance element connected electrically to said second common impedance element above said second common impedance element, and said first common impedance element and second common impedance element are opposite to each other, and are insulated from each other.
 2. A noise filter comprising a magnetic member formed by laminating magnetic sheets plural impedance elements formed in said magnetic member, and external electrodes formed at both ends of said magnetic member and connected electrically to each end of said plural impedance elements, wherein each impedance element is formed in vertical direction, the impedance element formed in the lowest layer includes a normal impedance element and a common impedance element connected electrically to said normal impedance element above said normal impedance element, the impedance element formed in the highest layer includes a common impedance element and a normal impedance element connected electrically to said common impedance element above said common impedance element, and other impedance elements have two common impedance elements mutually connected electrically and disposed in vertical direction, and the common impedance elements are opposite to each other and insulated from each other.
 3. A noise filter comprising a magnetic member formed by laminating magnetic sheets a first coil formed in said magnetic member, a second coil formed above said first coil, and external electrodes formed at both ends of said magnetic member and connected electrically to each end of said first and second coils, wherein said first coil includes a first conductor and a second conductor electrically connected to said first conductor above the first conductor, said second coil has a third conductor and a fourth conductor electrically connected to said third conductor above the third conductor, said first conductor and fourth conductor are spirally formed, and said second conductor and third conductor are opposite to each other, insulated from each other and spirally formed.
 4. A noise filter comprising a magnetic member formed by laminating magnetic sheets plural coils formed in said magnetic member in vertical direction, and external electrodes formed at both ends of said magnetic member and connected electrically to each end of said plural coils, wherein each coil is formed in vertical direction, and has two conductors electrically connected to each other, the conductors formed in the highest layer and lowest layer are spirally formed, other conductors are spirally formed, and further adjacent conductors not connected electrically are opposite to each other and insulated from each other.
 5. The noise filter of claim 3, wherein a distance between the second conductor and the third conductor is longer than 50 μm and shorter than 200 μm.
 6. The noise filter of claim 4, wherein a distance between the adjacent conductors not electrically connected is longer than 50 μm and shorter than 200 μm.
 7. The noise filter of claim 3, wherein a distance between the first conductor and the second conductor and the distance between the third conductor and the fourth conductor are longer than the distance between the second conductor and the third conductor.
 8. The noise filter of claim 3, wherein a material of low permeability is disposed between the first conductor and the second conductor, and between the third conductor and the fourth conductor.
 9. The noise filter of claim 1, wherein a length of the conductor between the external electrodes of the first impedance element is the same as a length of the conductor between the external electrodes of the second impedance element.
 10. The noise filter of claim 3, wherein a length of the conductor between the external electrodes of the first coil is the same as the length of the conductor between the external electrodes of the second coil.
 11. The noise filter of claim 1, wherein a density of the magnetic member between the first common impedance element and the second common impedance element is higher than the density of other potrtion.
 12. The noise filter of claim 3, wherein a density of the magnetic member between the second conductor and the third conductor is higher than the density in other portion.
 13. The noise filter of claim 1, wherein at least the first common impedance element and the second common impedance element are formed by electrocasting.
 14. The noise filter of claim 3, wherein at least the second conductor and the third conductor are formed by electrocasting.
 15. The noise filter of claim 1, wherein the first normal impedance element and the first common impedance element, and the second common impedance element and the second normal impedance element are formed so as not to overlap each other in a top view of the magnetic member.
 16. The noise filter of claim 3, wherein the first conductor and the second conductor, and the third conductor and the fourth conductor are formed so as not to overlap each other in a top view of the magnetic member.
 17. The noise filter of claim 1, wherein the first normal impedance element and the second common impedance element are connected to the external electrode formed at one end of the magnetic member, and the first common impedance element and the second normal impedance element are connected to the external electrode formed at other end of the magnetic member.
 18. The noise filter of claim 3, wherein the first conductor and the third conductor are connected to the external electrode formed at one end of the magnetic member, and the second conductor and the fourth conductor are connected to the external electrode formed at other end of the magnetic member.
 19. An electronic device, wherein the first impedance element and the second impedance element of the noise filter in claim 1 are connected to a pair of signal lines in a wireless communication device.
 20. A noise filter comprising a magnetic member formed by laminating magnetic sheets, a first coil formed by laminating plural first inner conductors, a second coil formed by laminating plural second inner conductors, and external electrodes formed at both ends of said magnetic member and connected electrically to each end of said first and second coils, wherein said magnetic member incorporates a first laminated body having said first inner conductors, a second laminated body formed on top of said first laminated body, having said first inner conductors and said second inner conductors laminated alternately, and a third laminated body formed on top of said second laminated body, having said second inner conductors.
 21. A noise filter comprising a magnetic member formed by laminating magnetic sheets a first coil formed by laminating plural first inner conductors, a second coil formed by laminating plural second inner conductors, and external electrodes formed at both ends of said magnetic member and connected electrically to each end of said first coil and said second coil, wherein said magnetic member incorporates a first laminated body having said first inner conductors, a second laminated body formed on the top of said first laminated body, having said first inner conductors and second inner conductors formed on a same plane, and a third laminated body formed on top of said second laminated body, having said second inner conductors.
 22. A noise filter comprising a magnetic member formed by laminating magnetic sheets, first and second coils formed in said magnetic member, and external electrodes formed at both ends of said magnetic member and connected electrically to each end of said first and second coils, wherein the area enclosed by the first coil and the area enclosed by the second coil are formed to overlap only in part in a top view of said magnetic member.
 23. The noise filter in any one of claims 3, 4, 20 to 22, wherein coupling coefficient is 0.2 to 0.95.
 24. The noise filter of claim 20 or 21, wherein an interval of the adjacent first inner conductors and the second inner conductors in the first laminated body and the third laminated body is larger than an interval of the adjacent first inner conductors and the second inner conductors in the second laminated body.
 25. The noise filter of claim 20 or 21, wherein a sheet of lower permeability than other magnetic sheet is formed between the adjacent first inner conductors and the second inner conductors in the first laminated body and the third laminated body.
 26. The noise filter of any one of claims 20 to 22, wherein a length of the first coil between the external electrodes is the same as the length of the second coil between the electrodes.
 27. The noise filter of claim 20 or 21, wherein a density of the magnetic member forming the second laminated body is higher than the density of the magnetic member forming the first laminated body and third laminated body.
 28. The noise filter of claim 20 or 21, wherein a distance between the first laminated body and the second laminated body and the distance between the second laminated body and the third laminated body are longer than the distance between the adjacent inner conductors of the first laminated body, the second laminated body and the third laminated body.
 29. The noise filter of claim 20 or 21, having a magenetic sheet of lower permeability than other magnetic sheets is formed between the first laminated body and the second laminated body, and between the second laminated body and the third laminated body.
 30. The noise filter of any one of claims 20 to 22, wherein electrically connected junctions of a pair of the external electrodes at one end of the magnetic member with the first coil and the second coil are disposed above or beneath, in a side view of the magnetic member, the electrically connected junctions of a pair of the external electrodes at other end with the first coil and second coil.
 31. An electronic device, wherein the first coil and the second coil of the noise filter in any one of claims 3, 20 to 22 are connected to a pair of signal lines in a wireless communication device.
 32. A noise filter comprising a magnetic member formed by laminating magnetic sheets, a first coil formed by laminating plural first inner conductors, a second coil formed by laminating plural second inner conductors formed alternately with said first inner conductors, and overlapping with said first coil in a top view of the magnetic member, and plural via holes formed in said magnetic sheets for connecting said first inner conductors mutually or said second inner conductors mutually, wherein said via holes for connecting the first inner conductors mutually overlap with said second coil in a top view of the magnetic member, the via holes for connecting said second inner conductors mutually overlap with said first coil in a top view of the magnetic member, and said first inner conductors and at least one of the second inner conductors adjacent to the first inner conductors are almost overlapping with each other in a top view of the magnetic member.
 33. The noise filter of claim 32, wherein said first inner conductors and said second inner conductors are formed in approximately U-shape.
 34. The noise filter of any one of claims 1, 3, 20 to 22, and 32, wherein the magnetic member is impregnated with fluorine silane coupling agent.
 35. The noise filter of claim 32, wherein said first coil has the same length as the second coil.
 36. An electronic device, wherein the first coil and the second coil of the common mode noise filter in claim 32 are connected to a pair of signal lines in a wireless communication device. 